Make a paste out of the turmeric, red chilli powder, vinegar, salt and pepper.
Add the fish and coat well. Leave it to marinate for around 15 minutes.
Heat oil in a frying pan and spread it across. Sprinkle in the curry leaves.
Fry the fish on both the sides till brownish and almost cooked. Switch off and leave in the pan.
In another saucepan, heat the oil for the masala. Add the onions and green chillies with a pinch of salt and cook till soft.
Add the ginger and garlic paste and saute till the raw smell is gone.
Add in the chopped tomatoes and cook till the tomatoes are mashed up.
Add all the powder and stir till the masala becomes slightly dark - ensure not to burn! Adjust the salt.
Add in a little water and cook for some more time on low flame till the masala is all cooked.
Slowly add the fish along with the oil and remains and stir softly to combine well, ensuring not to break the fish.
Cook on low flame for around 5 minutes on closed lid.
Switch off and serve warm with chapathis, or rice...