Place chicken breasts in the bottom of a 6-quart or larger crockpot.
Add black beans, corn, diced tomatoes, Rotel, chicken broth, taco seasoning, cumin, and chili powder to the crockpot.
Stir gently to combine ingredients around the chicken.
Cover and cook on LOW for 6 to 8 hours or on HIGH for 3 to 4 hours, until chicken is cooked through and tender.
Remove chicken from the crockpot and shred it using two forks. Return shredded chicken to the crockpot.
Stir the shredded chicken into the soup.
Ladle soup into bowls and garnish with fresh cilantro, crushed tortilla chips, shredded cheese, a dollop of sour cream, and sliced avocado, if desired. Serve hot.
Notes
For spicier soup, use Rotel with jalapeños or add a pinch of cayenne pepper. Adjust heat level to your preference.
Make your own taco seasoning with chili powder, cumin, paprika, garlic powder, and onion powder if you prefer.
The soup can be made ahead and reheated. Flavors improve overnight as they meld together.
Boneless, skinless chicken thighs can be substituted for even more moist results.