01 - Lightly grease the interior of a 6-quart slow cooker with cooking spray or oil.
02 - Arrange chicken breasts at the bottom of the cooker. Evenly coat with cumin, chili powder, garlic powder, salt, and pepper on all sides.
03 - Distribute diced onion, red bell pepper, frozen corn, and black beans evenly over the seasoned chicken.
04 - Pour 1 cup of enchilada sauce over the vegetable mixture, ensuring even coverage.
05 - Arrange half of the quartered tortilla pieces over the sauce. Sprinkle with 1 cup of shredded Mexican cheese blend.
06 - Add remaining enchilada sauce, followed by remaining tortilla pieces, and finish with the final cup of shredded cheese.
07 - Cover and cook on low heat setting for 4 hours, or until chicken reaches an internal temperature of 165°F and is fork-tender.
08 - Using two forks, shred the chicken directly in the slow cooker. Stir thoroughly to incorporate all ingredients. Recover and let stand for 20 minutes to allow flavors to meld.
09 - Portion hot casserole into bowls and garnish with fresh cilantro, sliced green onions, and a dollop of sour cream as desired.