Place the chicken breasts in the slow cooker. Add the chicken broth, diced tomatoes with green chilies, onion, garlic, black beans, corn, chili powder, cumin, salt, and pepper.
Stir everything together gently so the spices are distributed in the broth.
Cover and cook on low for 6 to 8 hours, until the chicken is fully cooked and easy to shred.
Remove the chicken breasts from the slow cooker. Shred them with two forks, then return the shredded chicken to the soup and stir well.
Ladle the soup into bowls. Top each serving with tortilla strips, avocado slices, cilantro, a squeeze of lime, and shredded cheese.