Cut the onion in half lengthwise, and then cut the halves into fine half rings.
Heat the oil in a heavy, wide, casserole-type pot over a medium flame. When hot, put in the onion and garlic. Stir and sauté for 2 minutes. Now put in the lentils and 3 cups of water. Bring to a boil. Cover, lower heat and simmer about 25 minutes or until lentils are just tender. Add the spinach leaves and roots, salt, and cumin. Stir to mix and bring to a simmer. Cover and simmer another 10 to 15 minutes or until spinach is tender and well-mixed into the lentils. Stir gently a few times during this period. Put in the black pepper and mix again. This dish may easily be made ahead of time and reheated.
Serves 6.
From "World-of-the-East Vegetarian Cooking" by Madhur Jaffrey