Score the pomfret and fry until golden brown, then let drain on paper towels. Cut the tomatoes into wedges. Sauté chopped onion and garlic until fragrant, then add the tomatoes and cook until soft, adding a little water if needed. Cut the fish into 3 pieces to help it absorb the sauce. When the tomatoes are soft, add the fish and simmer, turning the pieces over. Season to taste with sweet and sour flavors to your liking. When the sauce is just covering the fish, turn off the heat.