Grind the dry ingredients - grated coconut, turmeric powder, tamarind, peppercorns, coriander seeds and red chillies.
After this, add ground gravy and cook for 5 minutes. Add fish and cook for 10 minutes.
If needed add 1/2 cup water.
Let it get cooked for 10 minutes.
Switch of the gas/heat.
In a tadka pan or small pan, add oil preferably coconut oil. After the oil gets heated add chopped onion and fry till it gets slightly burnt. After onion turns brownish, give a tadka of burnt onion to the gravy and close the lid.
Add salt to taste. Remember that the fish was marinated with salt. So, add only 1/2 teaspoon salt first. Taste and add more if needed.