Clean and wash the fish and marinate with some salt and turmeric powder. Set aside for 5 minutes.
Heat oil in a saucepan/ kadai. Fry the fish until it becomes light brown. remove and keep aside.
Now put fenugreek seeds in the oil. After 5 seconds add cumin powder, salt, turmeric, pepper, chilli powder and 1/2 cup water. Cook the spices for about 4-5 minutes.
Add 2 cups water and bring it to boil over a medium heat.
Add fried fish and green chillies. Cover with a lid and cook until they become soft.
Clean and wash the fish. Marinate the fish with 1/2 tsp turmeric powder and some salt. Keep aside for 1 hour.
Heat up a saucepan/ kadai and add mustard oil. Fry the fish on each side for 3 minutes at medium heat till they are turn little brown. Take out gently after they are done.
Add mustard seeds in the remaining oil. After 10 seconds add chopped onion , salt, pepper powder and little turmeric powder and mix it well. Fry onions for 5 minutes with a little water on mid heat with a little water. Stir frequently.
Add 3 cups water or vegetable stock and bring it to boil.
Add the fried fish and green chillies. Cook it until fish getting tender/ soft on high heat.
Heat up a deep botton saucepan/ wok/ kadai. Add mustard oil and let it heat up properly. Fry the marinated fish both the sides well to crisp and brown. Take out and let it cool a little bit.
Now if you have some oil still left after frying, then do not throw it, add 2 tsp mustard oil more.
Temper this oil with fenugreek seeds and green chillies.
Then add all the masalas with some water. Fry it for 2 minutes at mid heat.
Now add 2 cups plain water and let the masalas cook for 5 minutes. stir occasionally.
Add the fried fish to the gravy. Cover it and cook for further 6-8 minutes or till the fish becomes soft.