Place tamarind and water in a small bowl. Let it soak for 10 minutes. Squeeze out tamarind and pass through a sieve. Discard solid bits. Set aside.
Place dried red chilies, coriander seeds, cumin seeds, black peppercorns, mustard seeds and fenugreek seeds in a small pan over low heat. Fry, stirring constantly, for about 5-6 minutes or until lightly toasted. Process to a fine powder. Add ginger, garlic, coconut, ground turmeric and tamarind pulp. Grind to a smooth paste. Set aside.
Heat oil or ghee in a large frying pan or skillet over medium heat.
Add onions and green chilies. Sauté, stirring occasionally, for about 2-3 minutes or until browned.
Add masala paste, curry leaves and water. Stir to combine. Season with salt. Bring to a boil. Simmer for about 3 minutes.
Add fish. Stir very gently. Cook, covered, for 10-12 minutes. Add more water if needed.
Garnish with curry leaves.
Serve this with:
Naan,
Rice, Neer Dosa,
Dosa,
Appam