Method of Preparation :
Grind the coconut, turmeric, kashmiri chillies and coriander seeds with little vinegar. When the paste is almost ready, add the ginger and cumin seeds and grind to a smooth paste. Keep aside.
Heat oil in a pan and saute onions till soft (not brown). Add green chillies, ground masala and the tamarind extract or mango slice. Stir over medium heat. Add 3 cups of water and cook till the gravy thickens a little. Add the fish pieces and salt. Cook till the gravy reaches the desired consistency and the fish is done.