Soak the tamarind in 2 cups of water and extract the juice. Grind together the chillies, coriander, pepper, cummin seeds and turmeric together and the coconuts separately. Crush the ginger, green chillies and garlic. Dilute the masala in the tamarind water.
Splutter the mustard, fenugreek and the curry leaves in oil and saute the crushed ingredients. Add the masala and tamarind water and salt. When it boils add the fish, put the lid on and let the curry simmer for sometime. Remove when the gravy thickness, serve with rice.