Rub the fish fillets with turmeric powder and some salt. Keep it for 10 minutes. You can also use with bone fishes like Rohu.
Heat the mustard oil in a pan.
Add the fish in hot oil and fry each side for 2 minutes. Remove those in a plate and crumble them with a fork. Do not make them mushy. If you are using with bone fishes then at this point discard the bones and skin, rest of the process will be same.
In the remaining oil, add chopped onion. Fry for 5 minutes.
Then add ginger garlic and green chili paste. Cook for 2 minutes.
Add all the spice powder and salt. Mix well.
Add the crumbled fish and mashed potato. Mix this very well for 4 minutes.
Add some salt and pinch of sugar. Mix well. Then add garam masala powder and chaat masala. Mix well for 2 minutes.
Lastly add chopped coriander leaves and green chilies. Mix well and turn off the heat.
Let this mixture come to room temperature.
Then make some small patties out of the mixture. You can give them any shape.
Take a bowl. Beat an egg with pinch of salt.
Now dip one patty in the beaten egg and then roll it in bread crumbs.
Again dip it in the egg and coat it with bread crumbs.
Let those coated patties rest for 15 minutes in the fridge.
Then fry those one by one in hot white oil for 3-4 minutes.
Remove them in a tissue paper.