Make the masala: Grind coconut, rice, green chilies, rasam powder, roasted sesame seeds with just enough water into a smooth paste.
Heat oil in a pan on medium flame, add mustard, cumin seeds and once the seeds start to splutter, add asafoetida and curry leaves.
Next add onions, peppers and cook till the veggies are slightly tender. Stir in the tamarind paste and salt. Cover and cook till the veggies are completely done.
Add the coconut paste and mix well. Bring the mixture to a boil and turn off the heat.