Preheat the oven to 375°F (190°C). Heat the oil in an oven-proof pan over medium-high heat. Add the onion and cook for about 8 minutes, until soft and browned.

Stir in half of the tomatoes and half of the Italian seasoning. Season with a pinch of salt and pepper. Place the tilapia on top of the mixture, then spoon the remaining tomatoes and seasoning over the fish. Add another pinch of salt and pepper.

Transfer the pan to the oven and bake for about 15 minutes, or until the fish is cooked through. Keep an eye on it to avoid overcooking.