Rinse moong dal thoroughly and soak in lots of water for 4~6 hours or overnight.
Combine the soaked dal with 4 cups of water, bring to a boil and cook uncovered, over medium heat. Skim off and discard the foam that forms on the surface.
Add the spinach, a little at a time to the pan. Cook till the spinach wilts. Cover and simmer, stirring occasionally, until the dal is almost tender but still firm-looking, about 20~30 minutes.
Uncover the pan, raise the heat to medium and continue to simmer the lentils, stirring occasionally, until the sauce thickens slightly and the spinach starts to look very soft, about 15 minutes.
While the curry is simmering, coarsely grind cumin seeds and chilies to a paste.
Heat the oil or ghee in a small skillet over medium-high heat. Add the onion and ginger, cook until onion is light brown around the edges, 5~8 minutes.
Stir in the cumin-chili mixture, tomato and salt. Simmer over medium heat, uncovered, stirring occasionally, until the tomato softens and gets mushy, about 3~5 minutes.
Add the sauce to the cooked lentils and mix well and cook for the flavors to mingle, 8~10 minutes, stirring occasionally. Serve and Enjoy!!