Lightly coat your 6-quart slow cooker with cooking spray. This prevents sticking and makes cleanup significantly easier.
In a medium bowl, combine enchilada sauce, diced tomatoes with green chilies, chili powder, cumin, and oregano. This creates the foundation of flavor.
Pour about 1/4 cup of the sauce mixture into the bottom of your slow cooker, spreading it evenly. This prevents your first layer of tortillas from sticking or burning.
Arrange tortilla quarters to cover the sauce.
Add half the chicken breasts.
Sprinkle half the black beans, corn, onion, bell pepper, and minced garlic.
Pour 1/3 of the remaining sauce over these ingredients.
Sprinkle with 1/2 cup of cheese.
Create a second identical layer with the remaining ingredients, following the same order: tortillas, chicken, vegetables, sauce, and another 1/2 cup of cheese.
Top with a final layer of tortilla quarters, remaining sauce, and reserve the last cup of cheese for later.
Cover and cook on HIGH for 3-4 hours or LOW for 6-8 hours. You'll know it's ready when the chicken is tender enough to shred easily with two forks.
About 30 minutes before serving, carefully remove the chicken pieces and shred them using two forks. Return the shredded chicken to the slow cooker, gently mixing it into the layers.
Sprinkle the remaining cup of cheese over the top, cover, and cook for an additional 15-30 minutes until the cheese is completely melted and bubbly.
Serve hot with optional toppings such as chopped cilantro, sliced green onions, diced avocado, sour cream, and lime wedges.