Add mustard seeds and when they crackle, add onions and stir for a while.
Add green chillies, ginger and shallot pieces and curry leaves. Stir for a few minutes.
Add tomato and fry them.
Add tomato puree and stir well.
Add salt, fenugreek powder, mango powder and fish masala.
Stir well.
Add coconut milk.
When it boils, add the fish pieces.
Stir slowly.
Cover it and cook on low-medium heat.
Stir once a while (careful not to break the fish pieces) until it is cooked.
Tips :
To clean fish nicely, put the fish pieces in cold water, add 1/2 cup of salt, a cup of vinegar, and 1 lime/lemon juice, and keep it for 15 minutes. This will take away the smell and the bad taste of fish.
***Note : Fish Masala *If you don`t have Kerala fish masala, then add 1.5 spoon [fine] coriander powder, 1 spoon chilli powder, 1/5 turmeric powder, one pinch more of fenugreek powder.