Cover the lentils with water and simmer for 15-20 minutes until tender.
Prepare the seasonings
In a frying pan, heat up oil on medium heat. When hot, add the mustard seeds, then the cumin seeds and stir.
As soon as they begin to pop they will get fragrant and add the chopped onion and garlic making sure to coat them well until they become translucent.
Add the coriander powder, salt, turmeric and chili and the tomato or tomato sauce and the cooked lentils. Stir and simmer for a few minutes.
Toppings
Top with chopped cilantro and black sesame seeds. Serve with white rice or flatbread.
Notes
You can make the soup with just coral lentils if you don't have any other lentils. Diced carrots and butternut squash are great additions too, along with some coconut milk if you want. It's all good!