Remove the innards of the fish and wash them. In heated oil, saute the chopped onion and garlic, salt, black pepper.
Add the chopped tomatoes without the skins, pour in sugar to kill the sour taste.
Cover with aluminum foil and bake in a preheated 392°F (200 °C) oven for 30 min. Remove the foil and put back in the oven to crisp for another 30 min.