Wash and drain the fish. Mix together the marinade ingredients and rub onto the fish. Allow it to marinate for 20 minutes.
Grind the ingredients for the paste adding sufficient water. Make sure it is smooth and thick.
In a pan, heat sufficient coconut oil. Fry the fish on both sides till golden, not necessarily fully cooked. Drain and set aside. Reserve the marinade.
In the same oil, add the onion, green chillies and ginger, and saute till wilted.
Add the tomatoes and curry leaves and cook till wilted and slightly browned.
Add the curry paste and saute for two minutes.
Add the fish along with half cup of water, mixed into the remaining marinade. Bring to boil and cook on low flame for around five minutes.
Now add the coconut milk, swirl the pan and switch off. Do not heat.
Serve with rice, appam, idiyappam, etc.