Add all ingredients except for lime juice in a medium pot. Bring to a simmer and simmer uncovered, over medium-low heat, for about 20-25 minutes. Stir occasionally. Mash the beans with a potato masher until the soup thickens (I leave the soup pretty chunky). Squeeze the juice of one lime in and stir. I generally don't need to add any salt. Serve with Corn Tortilla Chips, Sour Cream, Grated Cheddar Cheese and Sliced Green Onions.