Heat the ghee in a cooking pan. Add the whole masalas, ginger-garlic paste and green chillies and stir for few seconds.
Saute the onions till brown in the tempered oil. Add the chopped tomatoes with little salt and let them cook for a couple of min.
Add the turmeric powder, coriander powder and chilli powder. Cook till the raw smell disappears. It would take about 3-5min. Add the rasam podi and saute for another 3-5min. Add the water and bring them to boil.
Simmer the flame for another 10min.Switch off. Now add the coconut milk and salt. Mix thoroughly and squeeze in the lemon juice.
Garnish with coriander and serve hot with soup sticks/pepper papads.