Add dry beans and 2 cups water to a saucepan, cover and soak overnight. Drain and rinse before adding to slow cooker.
In a medium skillet, heat oil to medium-low and saute onion until tender, about 4 minutes. Add garlic and saute one additional minute. Add onion and garlic to slow cooker along with black beans, broth, tomato sauce, water, cilantro and cumin, stir.
Cook on low for 8-10 hours. It's done when the beans are tender. Add the remaining ingredients, stir and cook an additional 15 minutes. If preferred, use an immersion blender to make a creamier soup. We prefer the black beans whole.