Marinate the fish in the ginger garlic paste, lemon juice, and 1 TSP each of haldi and chilli powder. Keep aside for an hour

Heat oil in a frying pan and fry off the fish pieces till brown on both sides. Keep aside on a plate.

In a large, deep dish, heat a little oil. When warm, add the green chillies, curry leaves and black mustard. When it spitters add in the chopped ginger, garlic and the sliced onions.

Fry all this till the onions at slightly browned. Now add the tomatoes, 1 TSP each of the chilli and haldi powder and salt to taste. Let this cook on low heat, covered for few mins.

Pour in the Coconut milk, adjust the seasoning and let it boil for a while. You can add some water for a thinner gravy.

After few mins, add in the fish pieces and let this all cook for 6-7 minutes. Add the garam masala and vinegar and let it come to a boil. Taste and adjust seasoning if required. If you want it more sour, add a little more vinegar.

Take off the heat and serve with steamed rice and papad!