Start by preheating the oven to 175°C/350°F.

Prepare a medium sized baking dish by coating its bottom with a few tablespoons of the olive oil.

Pour the rest of the olive oil into a small bowl and mix it with the salt, pepper, oregano, garlic and tomato paste. Place the tilapia fillets in the baking dish. The skin side should be up. Use a spatula to gently spread the mix from the bowl over the fillets. A large part of the paste should be used to cover the centers of the fillets.

Slice one red or green pepper into thin slices. Slice one large onion into slices. Place the bell pepper and the onion slices around the tilapia fillets.

Place the baking dish in the oven and bake for 15 minutes. The baked tilapia is finished when you can easily flake it using a fork.

Remove the tilapia pan from the oven and place 1 tablespoon of butter on top of each fillet. Set the oven to broil and broil the tilapia for 5-7 minutes. The butter should be fully melted and just turning slightly brown when you remove the dish from the oven.