Soak the tamarind in half a cup of water for about 30 minutes. Grind the 5 green chillies, 2 garlic cloves and cumin seeds to a paste. Chop the remaining clove of garlic.
Heat the oil in a frying pan or saucepan and fry the onions until deep pink. Add the chopped garlic and the green chilli paste and fry for 3 minutes, stirring often.
Add the cumin, coriander, red chilli , garam masala and turmeric powders and stir constantly for a minute. Add the chopped tomatoes and fry for 4-5 minutes, stirring from time to time.
Add half the tamarind water, the jaggery, curry and coriander leaves and about 1 tsp salt. Taste and adjust the sour, sweet and salt flavours to your taste.
Add 3/4 cup of water and bring to the boil. Simmer for 5 minutes , then add the prawns and continue to cook for until the prawns are just cooked- this wont take long, 3-4 minutes. SErve immediately with rice and dal.