Greek Baked Fish With Tomatoes and Onions Recipe: Mediterranean Bake With Herby Tomatoes and Caramelized Layers

This Greek baked fish with tomatoes and onions recipe brings the flavors of Mediterranean coasts straight to your table, where tender white fish marries caramelized onions and bright tomatoes in a golden, herby embrace.

The secret lies in the slow baking process—15 minutes at 375°F—where the fish stays moist while the vegetables develop deep, sweet flavors.

I first discovered this technique while visiting a seaside taverna in Santorini, where the owner swore by the combination of olive oil, lemon, and oregano to elevate simple ingredients into something extraordinary.

The dish relies on just five key components: fresh fish (like branzino or cod), ripe tomatoes, sweet onions, and a trio of Greek staples—olive oil, lemon juice, and dried oregano.

The onions caramelize beautifully in the oven, their sweetness balancing the acidity of the tomatoes and the brightness of the lemon. What makes this recipe truly accessible is that it requires no fancy techniques—just layering, seasoning, and patience. The result?

A restaurant-quality bake that’s ready in under 30 minutes, perfect for a weeknight dinner or a special occasion.

By the time it emerges from the oven, your fish will be flaky and golden, the tomatoes tender with a hint of sweetness, and the onions caramelized to perfection. The aroma alone—warm herbs, citrus, and olive oil—will have everyone gathered around the table.

Serve it with warm crusty bread to soak up the juices or alongside a simple Greek salad for a complete meal. This is the kind of dish that feels like a vacation in every bite, without the travel.

For those who love flexibility, this recipe adapts easily—swap the tomatoes for roasted peppers, or add a sprinkle of feta cheese at the end for extra richness. The beauty of Mediterranean cooking lies in its simplicity and balance, and this dish delivers on both counts. Let’s get baking!

Ingredients for greek baked fish with tomatoes and onions

Five Mediterranean staples transform simple fish into restaurant-worthy Mediterranean flavor.

The fish makes all the difference here—branzino is my top pick for its delicate texture, but cod or halibut work beautifully too. Look for fillets with even thickness and vibrant color; Whole Foods or local seafood markets often carry the freshest cuts. If using frozen, thaw overnight in the fridge—never under running water, which turns fish mushy. The onions should be sweet, like yellow or red varieties, and the tomatoes ripe but firm. For extra authenticity, Trader Joe's carries excellent Greek tomatoes year-round. The olive oil matters too—opt for a light, fruity variety with a high smoke point, like Kalamata or Greek Koroneiki, to let the other flavors shine.

No fresh parsley? Dried parsley at half the amount works in a pinch, though fresh is ideal for that bright finish. Short on feta? Skip it or use a sprinkle of grated pecorino for a different but still delicious twist. The oregano is non-negotiable—Greek or Mediterranean blends have the right earthy notes, but regular dried oregano will do. For garlic, fresh is best, but if you only have powder, use half the amount. The lemon juice can be substituted with white wine vinegar if needed, though fresh lemon adds that essential brightness. And if you're feeling adventurous, swap the tomatoes for roasted red peppers for a different but equally delicious flavor profile.

This dish keeps beautifully—3-4 days in the fridge, though it's best eaten fresh. The fish reheats poorly, so plan to serve it immediately after baking. Store any leftovers in an airtight container with a paper towel on top to absorb excess moisture. For meal prep, assemble the dish ahead but bake it fresh—the caramelization happens during baking, so it won't be the same if pre-baked. The flavors actually improve slightly overnight, so if you're making this for a dinner party, assemble it in the morning and let it sit at room temperature before baking. The aroma alone will have guests anticipating the meal.

Step-by-step instructions for Greek baked fish with tomatoes and onions

Here's how to create a Mediterranean masterpiece with tender fish, caramelized onions, and herby tomatoes.

Preheat your oven to 375°F. In a large bowl, combine the 2 whole medium red onions that have been thinly sliced, the 4 whole Roma tomatoes that have been halved lengthwise and seeded, and the 4 cloves garlic that have been minced. Drizzle with 0.33 cup extra-virgin olive oil and sprinkle with 1 tbsp dried oregano, 1.5 tsp salt, and 0.5 tsp black pepper.

Toss everything together until the onions and tomatoes are evenly coated. Spread the mixture in an even layer on a rimmed baking sheet, making sure the vegetables are in a single layer. Bake for 20 minutes until the onions begin to soften and the tomatoes release their juices, creating a caramelized base. Here's the thing—you want the vegetables to soften but not fully cook through, so they'll finish baking with the fish.

While the vegetables bake, pat the 1.5 lb branzino or cod fillets dry with paper towels. This step is crucial for achieving crispy skin. Place the fish fillets skin-side down on top of the partially baked vegetables, slightly overlapping if needed to fit them on the baking sheet. Drizzle the fillets with 0.25 cup fresh lemon juice and sprinkle with any remaining dried oregano, salt, and black pepper.

Gently press down on the fillets to ensure they make good contact with the vegetables below. This ensures even cooking and prevents the fish from curling up. If you notice any gaps, use a small spoon to tuck the vegetables underneath the edges of the fish.

Return the baking sheet to the oven and bake for an additional 12-15 minutes until the fish is cooked through and the skin is golden brown. You'll know it's done when the fish flakes easily with a fork and the internal temperature reaches 145°F. The vegetables should now be fully tender, with the onions caramelized and the tomatoes softened but still holding their shape.

I always check for doneness by gently lifting one of the fillets with a spatula. If it releases easily from the baking sheet and the flesh is opaque throughout, it's ready. If the fish seems undercooked, return it to the oven for another 2-3 minutes. Overcooking is the biggest mistake here—it turns the fish dry and rubbery.

Remove the baking sheet from the oven and let the fish rest for 5 minutes. This resting period allows the juices to redistribute, ensuring each bite is moist and flavorful. While the fish rests, sprinkle the entire dish with 0.25 cup chopped fresh parsley and top with 0.25 cup crumbled feta cheese. The parsley adds a fresh finish, while the feta brings a briny tang that balances the dish.

Serve the Greek baked fish directly from the baking sheet, allowing guests to enjoy the caramelized onions and herby tomatoes alongside the flaky fish. The combination of tender fish, sweet onions, and juicy tomatoes creates a harmonious bite that captures the essence of Mediterranean cuisine. Pair with warm pita bread or a simple Greek salad for a complete meal.

Storing and reheating this recipe

Refrigerator Storage

This dish tastes best fresh, but leftovers keep well in the fridge for 2-3 days in an airtight container. The fish stays moist for 1 day if stored separately from the vegetables, which can last 3 days on their own.

I always store the components separately to preserve texture—fish reheats poorly, so it's best eaten within 24 hours of baking. 🧊

Freezer-Friendly Veggies

Save the vegetable base (onions, tomatoes, and garlic) for up to 2 months in the freezer. Spread them on a baking sheet, freeze solid, then transfer to a ziplock freezer bag with all air removed.

When ready to use, thaw overnight in the fridge and proceed with the recipe from Step 2. The fish, however, freezes poorly—it becomes dry and loses its delicate texture.

Reheating Leftovers

For the vegetable base, reheat in a skillet over medium heat for 5-7 minutes until warmed through. Add 1 tbsp olive oil and a splash of water to prevent sticking.

If you must reheat fish, use the oven at 300°F for 8-10 minutes—this keeps it moist better than the microwave. Cover loosely with foil to retain moisture.

Make-Ahead Tips

Assemble the dish completely but skip baking—store in the fridge for up to 12 hours before baking. This lets flavors meld beautifully. For a dinner party, prep the vegetables and fish separately, then assemble and bake just before serving. The aroma alone will wow your guests! 🌟

Serving Warm

Serve the dish straight from the oven at 165°F for optimal texture. If reheating, keep the oven at 350°F for 5-7 minutes to maintain warmth. The vegetables will soften further but retain their caramelized sweetness.

For best results, serve with warm pita bread or crusty sourdough to soak up the juices.

Frequently asked questions