Clean, wash, and cut the mackerels into medium pieces. Marinate the fish pieces with turmeric powder, red chilli powder, and salt and keep it aside. Heat oil in a pan. Add half of the chopped onions and saute until light brown. Add the grated coconut and fry until golden brown. Transfer this into a bowl and keep it aside to cool.

In the same pan, dry roast the dry red chilies, coriander seeds, peppercorns, urad dal, fenugreek seeds, & raw rice until light brown. Make sure not to burn it. Remove from flame and allow it to cool. Once cooled, grind all the roasted ingredients into a fine paste adding the tamarind pulp.

Heat oil in a claypot. Add the remaining chopped onions and saute until translucent. Add the prepared ground paste and fry for another 4-5 mins. Add water as needed and allow it to boil. Once the gravy starts to boil, add the mackerel pieces and mix gently. Cook on low-medium flame for 10-15 mins, gently stirring occasionally. Continue to cook until the fish is cooked well. Serve hot with steamed rice or chapati.