Heat oil in a large skillet over medium heat; add chicken and onion. Saute 10 minutes, or until chicken is cooked through; set aside.
Combine broth, beans, undrained chiles and seasonings in a large Dutch oven. Bring to a boil over medium-high heat. Add chicken mixture; reduce heat and simmer 30 minutes. Add sour cream, stirring well. Top each serving with shredded cheese; garnish, if desired.