In a mixer grinder jar, add grated coconut, spices – black peppercorns, dry red chilies, marble size tamarind ball, coriander seeds and turmeric powder along with 1 cup water and grind to make thin smooth paste or gravy.
Heat a curry pan or kadai(wok). Add oil. After oil gets heated, add finely chopped onion, slit green chilies and sauté till onion turns brownish.
Pour the gravy from the mixer jar into the kadai and stir well. If the gravy is thick, add ½ cup water and simmer.
Once the curry starts boiling, add the fish pieces.
Cook on medium heat for 4-5 minutes.
Add salt to taste and stir gently, else the fish pieces will break.
Switch off the gas.
Cover and keep for at least 10 minutes before serving. The fish will continue to get cooked in the hot curry.