Wash the lentils and rinse a couple of times. Be careful to remove any stones. If you have time, soak the lentils in water as long as you can, up to overnight, before you cook. They get very soft and cook faster.
Start rice preparation according to package directions.
Prep the onion, garlic, ginger, tomatoes, and cilantro/green onion and set aside.
Heat oil on high. Add ginger, garlic and onion, and stir fry on high until the onion is a little brown on the edges, 1-2 minutes. Stir in cumin seeds, salt , turmeric, mustard seed and coriander powder. Turn the heat down to medium and cook for 2 minutes, stirring often. Add tomatoes and butter. Stir, cover with lid and cook for 4 minutes. Stir in the lentils, cover and cook for 5 minutes. After cooking for 5 minutes, add one cup of water, cover with lid and cook for 5 more minutes. When the 5 minutes are up, stir in 2 more cups of water, as the water will begin to decrease as you cook. Continue cooking on medium for 10 minutes. The dal should be cooked and ready to serve. If not tender, cook a little longer, adding more water if necessary.
Sprinkle the chopped cilantro and/or green onion on top of the dal and serve with or on top of the rice. It is typical to serve with chutney or spicy peppers.