Clean and drain the fish properly. If it is a full flat fish, then slice into pieces. Make a fine paste of ginger and pepper, mix with the chilli powder, turmeric powder, salt and vinegar. Add few teaspoons of water to make a thick, smooth paste. Apply this mix on both sides of the fish slices as a very thin layer. Keep aside for 30-45 minutes. Deep fry the fish pieces on either side until golden brown. Drain the oil.