Fillet the fish and clean. Fry onion, ginger, garlic and green chillies in vanaspathi. Before it gets brown add Melam fish masala. After 7 minutes add tomatoes, salt, vinegar and cooking sauce. Fry well. Then put the fish slices on the top of the masala. Put some of the masala over the fish and allow it to boil for 5 minutes. Then place the masala fish on a flat dish and bake for ½ hour or till it gets brown.