Marinade pomfret medium pieces with salt and turmeric powder. Keep aside for half an hour.
In hot water, add garlic n ginger paste,cumin powder, cilantro powder. keep aside.
In a pan add 2 tsp oil and fry the pieces over medium heat both sides till crisp. Keep aside.
In another pan, add 2 tsp oil. Do not use the same oil in which you fry the fish. Add mustard seeds , let it sizzle. Add chopped onion till golden brown. red chile powder, turmeric powder ,fennel seed powder. Add chopped tomatoes . Mix well for 4 mins till tomatoes soft.
Add hot water mixture into it and simmer for 15 mins at low heat. When gravy gets thick, add fried fish and simmer further for 5 mins. When perfectly done ,Add salt to taste and sprinkle fresh cilantro leaves and lemon juice just before serving.