1. Wash, de-vein and drain the water off the prawns completely and keep aside. 2. Make a coarse paste with green chillies, garlic, ginger and coriander leaves and keep aside. 3. In a mixing bowl, add 1 large sized sliced onions, turmeric powder, garam masala, salt to taste, red chilli powder, green chilli coarse paste, little oil and mix all the ingredients well. 4. Heat oil in wide mouth big pan, when the oil is hot enough, add the onion masala mixture and sauté well for about 3-4 minutes. 5. Add the prawns and stir well so that the masala is nicely coated with the prawns. 6. Allow to cook in its own juices (do not add water at all). 7. Add little chopped tomato pieces and mix well so that they get mashed completely. 8. When the oil oozes out from the sides and all the moisture is dried up, then add chopped coriander leaves, stir and switch off the flame.