1. Rub the prawns with some salt and a pinch of the turmeric powder.
2. Keep if for 5 minutes then wash well and drain.
3. Rub the ground paste into the prawns and marinate the mixture for few minutes.
4. Heat the oil in a heavy-bottemed pan and drop in the curry leaves.
5. Add the chopped onions and saute on medium heat for about 3 minutes or till the onions are light brown.
6. Add the tomato pieces and fry till the oil leaves the sides.
7. Add the prawns along with the marinade and stir fry briefly.
8. Add the chopped green chillies, salt sugar and vinegar to taste.
9. Mix well and cover and cook on low heat for about 10 minutes or till the prawns are cooked and the oil starts floating on top.