Thoroughly rinse the lentils. Place them in a pot with the water and bring to a boil. Cook until soft – about 30 minutes.
Meanwhile, heat oil in a heavy bottomed pot, and cook mustard seeds until they begin to pop. Add the cumin seeds, garlic and curry and sauté for a few secs. Add the chopped onions, ginger and green chilies, if using, and sauté until onions are translucent.
Add the chopped tomatoes and stir-fry for 4-5 minutes; then the turmeric powder and sea salt; and stir to combine.
Finally, add the cooked lentils to the onion-tomato mixture along with 1 cup water and cook for another 10 minutes on low-medium heat until texture is soft and soup like. Serve over rice or with naan.