Cut and clean the fish. Wash with salt and keep it aside.
For the masala, grind the chillies, jeera, turmeric powder, garlic, onion, tamarind, coriander seeds and 5 tbsp of grated coconut to a fine paste.
Remove the skin of the potatoes and cut into pieces. Boil the potatoes and keep it aside.
Keep a wok and add the masala. Add extracted coconut milk and give it a boil. Let the gravy be semi thick.
Add two sliced green chillies, vinegar and salt to taste.
Add the fish, when it starts boiling, add potatoes.
Serve hot with panpales, rice.