If you have time, caramelize the onions in the butter (in large skillet). If not, sauté them until tender. Add the curry powder, lentils, water, tomatos, and spices to the skillet. Simmer until lentils are tender, about 15-25 minutes. In a separate skillet, lightly sauté the pressed garlic (in a little olive oil or just with water) and then add the spinach to wilt it. Add the wilted spinach/garlic mixture to the lentils, stir, and serve over rice.
Adapted from Jen Johnson