Heat oil in a large pot over medium-high heat. Add onion, garlic, sweet potato and bell pepper; cook, stirring occasionally, until the vegetables are slightly softened, 5 to 6 minutes.
Stir in chili powder, cumin and oregano and cook, stirring, until fragrant, 1 minute.
Add beans and broth (or stock) and bring to a boil. Reduce heat, partially cover and simmer gently for 15 minutes.
Increase heat to medium-high and stir in corn; cook 1 minute.
Add chicken and cook until heated through, 1 to 2 minutes more.
Remove from heat. Stir in salt and pepper. Serve topped with sour cream, avocado and/or cilantro, if desired.