Heat a little oil in a pan and add chopped onions to it. With the onions saute ginger garlic paste and chopped green chillies and add chopped tomatoes. Mix everything with salt, all ground spice, coriander powder and red chilli powder. Pour a little water and mix the masala well. Add a little kokam into the masala. Add prawns and mix them well with the masala. Allow the prawns to cook for some time. Your Jhinga Masala is ready. Transfer it to a serving plate. Garnish it with onion slices and chopped coriander.