Marinate the prawns with 1 tsp chilli powder, turmeric powder and salt. Keep it aside for 1 hour. Then fry it till golden brown. Keep the fried prawns aside. In the same oil, add mustard seeds once it splutters, add the ginger-garlic paste and when the raw smell goes off, add the shallots and saute till golden brown. Add the curry leaves and then chopped tomato and saute till it becomes mushy.