Chop up one onion and two tomatoes and heat it in pan until in turns into a translucent paste. To this add chilli powder, turmeric powder, coriander powder, lemon and salt and mix well. Now take another skillet and add ginger garlic paste and heat in oil for about a minute until it turns brown.
Now to this add the the gravy you cooked previously, to this add water as needed. Mix well and boil. After 5 minute add the fish to the mixture and cook for about 25 minute. Wait untill the curry cools down a little before serving. Serves well with rice.