Clean, wash and cut fish into one and half inch thick slices and pat dry with an absorbent towel. Mix lemon juice with a little salt, apply on the fish slices and keep aside. Peel and finely chop onion. Clean, wash and chop fresh coriander leaves. Peel garlic.
Soak tamarind in one cup of warm water for half an hour, remove the pulp, strain and keep aside.
Dry roast peppercorns, garlic, red chillies and coriander seeds separately and grind to a paste along with scraped coconut. Heat oil in a pan, add chopped onion and stir-fry for two minutes or till translucent.
Add masala paste and turmeric powder and sauté for two to three minutes. Add two cups warm water, tamarind pulp and salt. Bring it to a boil, reduce heat and cook further on medium heat for three to four minutes. Gently slide in the pomfret slices and cook on medium heat for four to five minutes or till the fish is firm and cooked. Stir in coconut milk, reduce heat and simmer for a minute.
Garnish with chopped coriander leaves and serve hot accompanied with steamed rice. You can replace pomfret with any other fish.