Wash and dry the fish and cut into serving pieces.

Soak tamarind pulp in vinegar until softened.

If tamarind is very dry, heat it briefly in an enamel saucepan with a little water.

When cool enough, squeeze the tamarind in the liquid to dissolve the pulp.

Strain the mixture through a fine sieve, discarding seeds and fibers.

Place all ingredients (fish, tamarind mixture, onion, garlic, ginger, salt, curry leaves, lemongrass, cinnamon stick, fenugreek seeds, black pepper, chili powder, water, and oil) in a pan.

Bring the mixture to a boil.

Reduce the heat to low and simmer uncovered until the fish is cooked through and the gravy has thickened.

Shake the pan or carefully turn the fish pieces occasionally during cooking to ensure even cooking.

Serve hot with white rice.