01 - Lightly grease the inside of a 6-quart crockpot with cooking spray or a small amount of oil.
02 - Place the chicken breasts in the bottom of the slow cooker. Sprinkle evenly with cumin, chili powder, garlic powder, salt, and pepper, pressing the spices into the meat.
03 - Layer the diced onion, red bell pepper, frozen corn, and black beans over the seasoned chicken.
04 - Pour 1 cup of enchilada sauce evenly over the vegetable and bean mixture.
05 - Arrange half of the quartered tortilla pieces over the sauce, creating an even layer. Top with 1 cup of shredded Mexican cheese blend.
06 - Repeat the layering process: pour the remaining enchilada sauce over the cheese, add the remaining tortilla pieces, and finish with the remaining 1 cup of shredded cheese.
07 - Cover and cook on low heat for 4 hours, or until the chicken is cooked through and tender (internal temperature reaches 165°F).
08 - About 20 minutes before serving, uncover the slow cooker and shred the chicken directly in the pot using two forks. Mix thoroughly to incorporate all ingredients, then cover and let sit to meld flavors.
09 - Serve hot, garnished with fresh cilantro, sliced green onions, and a dollop of sour cream if desired.