In the cooking pot, add the fish pieces, Cayenne Pepper, Paprika, turmeric and salt and mix well. Marinate for 10 minutes.
While the fish pieces are left to marinate, roughly chop the tomatoes and slit the Serrano pepper length wise. If the kokum you have is dry, soak it in a little water.
Add the chopped tomatoes, Serrano pepper, and kokum to the marinated fish pieces, add enough water to cook the fish.
Grind coconut and ginger with very little water into a smooth paste using a food processor or indian style mixer grinder.
Once the fish pieces are cooked, add the ground coconut paste. Add more water (if required) to adjust the consistency and also adjust the spices.
Bring to a boil and garnish with curry leaves. Serve hot with rice.