Heat 2tsp oil in a saucepan, add the cumin seeds and once the seeds start to turn dark, add the onions and cook till they turn translucent, about 3~5 minutes.
Add the ginger and saute for 30 seconds.
Stir in the tomato puree, chili powder and salt. Simmer for 5~8 minutes.
Gently stir in the coconut milk. Simmer the soup till all the flavors get a chance to mingle. If the soup seems too thin, then stir in rice flour that is whisked in water and simmer the soup for 2~3 minutes or till the soup is thick.
Garnish with cilantro and serve with grilled cheese sandwich.