Soak and cook the black and red beans according to package instructions. In a Dutch oven, place your lentils and add 6 cups of broth. Gently simmer with lid titled on top for about 15 minutes. While the lentils are simmering, in a saucepan, add the oil and then sauté the onion and garlic. Mixture. After the lentils have been cooked, add the onion and garlic mixture. Then add the taco seasoning, tomatoes, cooked black beans and cooked red beans. Bring to boil and simmer for 10 minutes. Make sure you do not overcook the lentils or they will become mushy. Sprinkle cilantro on top. Optional: can serve with light sour cream.