Fish in mustard gravy(Machcha Besara)

1. Clean the fish pieces properly, and marinate it with half tsp salt, half tsp turmeric, 2tsp lemon juice, half tsp chilly powder, half tsp ginger-garlic paste and keep it aside for half an hour. 2.In a bowl, soak 1 tsp mustard seeds, 1 tsp cumin seeds, 1 dry red chili pepper, garlic cloves in very little amount of water for half an hour. Chop one tomato into small pieces. After half an hour, in a blender grind tomato pieces along with the soaked mixture of mustard seeds,cumin seeds, garlic cloves,red chili pepper and make a paste. 3. Add 2 tsp oil to a pan and once the oil gets heated, shallow fry the marinated fish pieces and once completely fried, keep them aside. 4.In the same pan, add 2 more tsp oil.Chop one onion and add to the oil. 5.Once the onions are golden brown in color, add the paste made in step 2 with the fried fish pieces. Add 1 tsp of salt and half tsp of turmeric powder along with 1 cup of water and cook it on low to medium flame for 20-25 minutes, till the raw smell of mustard and garlic is gone. Add the salted dry mango towards the end of cooking. Serve the fish gravy with plain white rice.The taste is amazing.