Heat oil in a deep vessel. Add mustard seeds, as they splutter add onions, curry leaves and sauté till onions are translucent. Add asafetida.
Rinse the lentils with water and add into the vessel.
Add water, tomatoes, salt and chili powder. Close the lid and let it cook on medium heat.
Once cooked, garnish with chopped cilantro.
Serve with nan or with plain white rice.