In a large Dutch oven (4 to 6 quarts) or stockpot, heat 2 tablespoons of olive oil over medium heat. Once hot, add the sweet potatoes, onion, and bell peppers. Saute for 3 - 5 minutes, stirring frequently, until the onions are translucent and the peppers are slightly softened.

Pour 2 cups of broth into the pot and then add all of the remaining ingredients (beans, tomatoes, and seasonings). Add the remaining broth if necessary (about 1 cup more) so that the contents of the pot are almost completely covered by liquid.

Bring the pot to a boil and then reduce the heat to maintain a gentle simmer. Cook uncovered for 45 minutes - 1 hour, stirring occasionally. The sweet potatoes should be tender and the liquid reduced. Add a splash more liquid (broth or water) if you find that the chili is getting too dry.

For a thicker chili, use a potato masher (or fork) to mash the chili to your desired consistency. For a thinner chili, add in more broth (or a splash of water).  

Serve warm, optionally topped with cilantro, avocado, fresh lime slices, and a side of tortilla chips.