Sprinkle a little gram flour, salt and some vinegar on the fish pieces and rub well. Keep aside for 5 minutes and then wash well. Rub in the rest of the vinegar and keep aside for 15 minutes. Remove from the vinegar and pat dry well. It is important that the vinegar is removed from the fish pieces by gently wiping them repeatedly with an absorbent kitchen towel.
In a bowl, mix the rest of the ingredients and rub well on the fish pieces. Marinate for about half an hour.
Heat the oil till it is very hot. Slide in the fish pieces and deep-fry in batches till they are crisp and golden brown in color.
Garnish with lemon wedges.