Grind onion, dry red chillies, garlic, ginger, and green chillies into a coarse paste.

Marinate the fish with lemon juice, turmeric powder, and salt for 15 minutes.

Heat coconut oil in a flat skillet, add curry leaves, and let them crackle.

Add the ground onion paste and stir until the raw smell disappears (low flame).

Add turmeric powder and tamarind water, stir well.

Let the water reduce, then gently place the marinated fish pieces in the gravy.

Sprinkle salt and pour in half of the coconut milk, stir gently.

Cover and cook for 10 minutes.

Add the remaining coconut milk, cover, and cook for another 20 minutes.

Check for salt and stir gently before serving hot.