Combine all the ingredients listed under "for marination". Add cleaned fish pieces to this.
Marinate the fish pieces for half an hour.
Heat 1-2 tbsp oil in a tawa. I used cast iron tawa, you can use a non stick tawa or a shallow frying pan.
Fry both sides of the fish pieces till it's half cooked. Transfer the fish pieces to a plate.
In the same pan, heat 1 tbsp oil and add crushed pearl onion, ginger and garlic. Fry for 3-4 mins or till it turns golden.
Add the masala powders (listed under "for masala"). Cook for 2-3 mins or till the raw smell goes.
Add salt and tamarind paste and mix well. Add coconut milk (start with 1/3 cup) and mix gently.
Add the fish pieces and make sure each piece is coated well with the masala. Add more coconut milk, if required.
The curry is ready when the consistency is semi-dry and the fish pieces are coated well with the masala.