Heat a large 6 or 8-quart pot over medium heat. Add a small amount of broth to coat the bottom of the pot, and then add onions and sauté for about 4-5 minutes. Add additional broth as needed to keep onions from sticking to the bottom of the pot.
Next add the garlic, spices, salt, and sweet potatoes, and sauté for an additional 2-3 minutes. Add the fire roasted tomatoes, broth, and water, and simmer the soup uncovered for about 15 minutes until the sweet potatoes are nearly fork tender. Add in the beans and cook for 5 more minutes until beans are thoroughly heated. Remove soup pot from heat and add lime juice. Taste and adjust salt, spices, and lime if necessary. Garnish with toasted pumpkin seeds or avocado.