Rinse the fish fillets. Frozen fish should be lightly thawed. Rinse and clean and finely slice the onion. Clean and thinly slice the pepper. Slice the tomatoes. Put a small amount of margarine in a baking dish. Melt this in the oven. Spread the chopped vegetables in the baking dish. Add the cod or haddock fillets. Mix the margarine with the parsley,the pressed garlic clove,salt and the pepper. Click the aromatic butter over the fish. Cover the dish with aluminum foil. Cook the dish in the oven at 225 degrees C about 20 min. Serve with potato and fresh sliced cucumbers.