Heat oil in meen chatti, add mustard and fenugreek seeds. When it splutters add chopped onions. Saute till it becomes brown.
Add ginger, garlic and green chillies. sauté for 2 minutes.
Add tomatoes, chilli powder, turmeric powder and coriander powder. Sauté for a minute.
Add 1 cup water and boil for 2 minutes.
Then add fish pieces to this gravy and mix well.
Close meen chatti with a lid and cook for 10 minutes, until fish is cooked and gravy becomes thick.
Then add salt and kudam puli to this and cook for another 5 minutes in a low flame.
Now Kerala fish curry is ready to serve with fish and kappa.