Soak cocum (kudampuli) in 4 tablespoon salted luke warm water for 15 - 20 minutes.
Heat oil in a pan. Saute small onion , ginger , green chilly and curry leaves.
Once onion turned light brown, add turmeric, chilly and coriander powder. Keep it in low flame. Saute it well.
Add thick and medium coconut milk. Add water in which cocum was soaked. Taste the mixture and add soaked cocum pieces as required. Add enough salt. Keep it in low flame.
Bring it to boil and then add cleaned fish pieces. Cook it till fish gets cooked and gravy is consistent. It would take around 20 minutes.