Clean and slice the fish pieces and keep in a bowl.
Add red chilly powder, turmeric powder, salt and 2 cups water to it. Mix well and keep aside.
Meanwhile grind coconut with 2 shallots, cumin seeds and enough water. Keep this aside.
Take all the ingredients in a plate: chopped tomatoes, remaining shallots, chopped ginger and bird's eye chilly. Keep this aside.
Heat oil in a claypot and add mustard seeds and fenugreek seeds. When it starts to splutter, add shallots and saute well till shallots become light brown in colour.
Add tomato, bird eye chilly, ginger and curry leaves. Saute it again for 5 minutes.
Add fish and previously prepared masala water to it and cook it for 10 minutes till fish is done.
Add coconut paste into the curry.
Mix it well. Mix in a medium flame and when it starts to boil, turn off the flame.
Serve hot with rice.