Peel and cut the sweet potatoes into small, evenly sized cubes. Dice the onion and bell pepper, then mince the garlic.
Heat the olive oil in a large pot or Dutch oven over medium heat.
Add the diced onion and bell pepper. Cook for 4–5 minutes, stirring occasionally, until the vegetables begin to soften.
Add the minced garlic, chili powder, cumin, smoked paprika, salt, black pepper, and cayenne pepper if using. Stir and cook for about 30 seconds.
Add the cubed sweet potatoes and stir until they are well coated with the spices.
Pour in the diced tomatoes and vegetable broth. Stir everything together.
Bring the chili to a gentle boil, then reduce the heat to low.
Cover partially and simmer for about 25–30 minutes, stirring occasionally, until the sweet potatoes are nearly tender.
Add the drained and rinsed black beans. Stir well and continue cooking for another 5–10 minutes.
Check that the sweet potatoes are fork-tender and taste the chili. Adjust the salt and spices as needed.
If the chili is too thick, add a little vegetable broth. If it is too thin, simmer uncovered for a few more minutes.
Serve hot with fresh cilantro, avocado, shredded cheese, sour cream, or your favorite chili toppings.