Clean and wash the fish pieces well. Pat dry.
Take the fish pieces in a medium bowl and sprinkle salt, turmeric and chili powder. Lightly rub the spices on the fish pieces and allow to marinate for about 15 minutes.
In the meantime, soak a little tamarind in ½ cup of water for about 10 minutes; then squeeze the tamarind to extract the juice and keep aside. You can also use tamarind paste.
Then chop the onions, tomatoes and coriander leaves finely. Slit the green chillies.
Heat oil in a frying pan and shallow fry the fish pieces on both sides until they turn slightly brown. Remove and keep aside.
Sizzle mustard seeds, cumin seeds, fenugreek seeds and fennel seeds in the same oil.
Then add the finely chopped onions, green chillies and a teaspoon of salt and sauté till the onions turn brown.
Tip in the ginger garlic paste and fry till the raw small goes away.
Next put in the chopped tomatoes and mix well. Cover with a lid and cook till the tomatoes become mushy.
Now add all the spice powders - turmeric powder, Kashmiri chili powder and coriander powder. Mix well and cook on low heat till the oil separates.
Pour 2 tbsp. of tamarind water or tamarind paste and about 1 cup of water. Simmer over medium heat for a couple of minutes.
Then add the lightly fried fish pieces and simmer over medium heat till done.
Finally garnish with coriander leaves.
Serve Tomato and Tamarind Fish Curry with steamed rice!