In a large pot, heat the olive oil over medium heat.
Add the chopped onion and cook until translucent, about 3-4 minutes.
Add the minced garlic, chili powder, cumin, paprika, and cayenne pepper.
Cook for another 1-2 minutes until fragrant.
Add the diced sweet potatoes and red bell pepper to the pot.
Season with salt and pepper.
Cook for about 5 minutes, stirring occasionally, until the sweet potatoes start to soften.
Pour in the vegetable broth and diced tomatoes with their juices.
Stir everything together.
Bring the mixture to a boil, then reduce the heat to low.
Cover the pot and let the chili simmer for about 15-20 minutes, or until the sweet potatoes are tender.
Add the black beans to the pot and stir to combine.
Let the chili simmer for an additional 5-10 minutes to allow the flavors to meld.
Taste the chili and adjust the seasoning with more salt, pepper, or spices as needed.
Serve the sweet potato and black bean chili in bowls, and top with your choice of optional toppings like chopped cilantro, shredded cheese, sour cream, or diced avocado.