Soak tamarind in ½ cup water and strain, reserving the water.
Mix fish pieces with ginger, chopped onion, 2 green chillies, coriander leaves, turmeric powder, some water, and salt in a large saucepan. Cook on medium heat until the fish turns tender.
Strain the mixture, separating the fish and stock. Mash the boiled fish and keep aside.
Grind together all the ingredients of grounded masala.
Separate the egg yolk and white. Beat the egg white well.
Mix mashed fish with egg yolk, bread, pepper powder, maida, and 1 tsp oil. Shape the mixture into medium-sized balls.
Heat oil in a pan. Dip the balls in the egg white and fry them until golden brown.
Heat the remaining oil in a separate pan and fry sliced onion, remaining 2 green chillies, and curry leaves.
Mix in ground masala and cook well.
Pour in fish stock, tamarind water, sugar, and salt. Stir and simmer.
Put in fish balls and cover the pan. Cook on low flame until the curry thickens and oil floats up.