First heat the oil in a flat pan with a lid. Add onions, green chillies, ginger garlic paste and curry leaves until lightly browned.
Add coriander powder, pepper powder, cumin powder, turmeric powder, garlic and fry on low flame for 5 minutes. Push the mixture to the side of the pan and place the fish in a single layer in the center of the pan. Spread the paste over the fish.
Pour the coconut milk and cover the pan with the lid and cook for 10 minutes. Lightly loosen the fish by gently shaking the pan a few times while cooking.
Pour little more of coconut milk if required and sprinkle salt. Place slices of tomato and simmer for 5 minutes more and remove.
Serve with Appam.
If you want to know more Kerala Recipes then find by typing in this search box.