Heat olive oil in a skillet over medium-high heat. Cook and stir chicken and onion in hot oil until the chicken is no longer pink in the center and the juices run clear, 7 to 10 minutes.
Stir refried beans, corn, chicken broth, taco seasoning, picante sauce, and garlic powder together in a slow cooker; add the chicken and onion mixture.
Cook on Low until the chicken pulls apart easily with 2 forks, 3 to 5 hours. Shred chicken in the soup with 2 forks. Continue cooking for 1 hour more. Ladle into bowls and top with Cheddar cheese.
