In a large heavy bottom pot over medium-high heat, heat the olive oil. Add the onions, sweet potatoes, bell pepper and garlic. Stir to combine, and cook until the onions are translucent and the vegetables soften, about 5-7 minutes.
Add the chili powder, smoked paprika, cumin, oregano, salt and pepper, and stir to coat the vegetables.
Pour the vegetable broth, black beans, diced tomatoes with their juices and chopped green chilis with their juices. Stir to combine and bring mixture to a boil.
Cover the pot and reduce the heat to maintain a gentle simmer. Cook for 30-35 more minutes, stirring a couple times until the vegetables continue to soften and the mixture thickens.
Ladle into bowls and serve with diced avocados and fresh cilantro, if desired.