In a large pot, saute the onions, garlic, and bell pepper until the onions soften, about 3 minutes.
Add the beans, seasonings, and tomatoes, and stir to combine. Add 3 cups vegetable broth or water. Reduce the heat to a simmer, and cook, uncovered, for about 1 hour, adding additional water or vegetable broth as needed to keep a soupy consistency.
Just before serving, add the corn, if you like, and heat through. Serve in bowls with lime wedges. Makes 4-6 servings.