Add oil to a deep bottomed pan and heat. Splutter mustard seeds first. Add the onion pieces, fry for some time and add the onion paste. Fry until the contents turn brown.
Add the tomato pieces and cook until they are tender. Add the marinated fish pieces, drumstick pieces, red chilly powder, coriander powder and salt. Stir well and fry until oil separates. Add water, mix well and cook until the fish is done.
Top the preparation with finely
chopped coriander leaves and serve hot with rice.