Heat a pan with oil. Fry the onions until they turn golden brown.
Add the onion, ginger and garlic pastes. Stir and add the turmeric, red chili and coriander powders. Pour in 1/2 cup of water
Cook until the water released dries to form a thick gravy with oil floating on top.
Add the fish slices. Also add the mustard paste. Turn over the sides of the fish slices and stir the mixture so that spices cover the fish well
Pour in 1 cup of water and sprinkle the salt.
Cook with lid on at low heat for 10 minutes.
Sprinkle the coriander leaves and green chilies. Cook for another 5-7 minutes.