Cut the fish lengthwise, remove the main bone and skin. Cut the pieces 3/4″ (2 cm) thick, season, sprinkle it with a little black pepper and set it aside.
Cook for 10 minutes on low heat, stirring often. Spread half of the sautéed vegetables in a baking dish, spread the fish fillets on top and cover with the rest of the mixture.
Bake for about 15 minutes in the oven at 356°F (180 °C).