Place the chicken breasts in the bottom of the slow cooker.
Add the enchilada sauce, diced tomatoes with green chilies, black beans, corn, onion, garlic, and taco seasoning. Stir to combine around the chicken.
Cover and cook on low for 6 hours or high for 3 to 4 hours, until the chicken shreds easily.
Remove the chicken, shred with two forks, and return it to the slow cooker.
Stir in the torn tortilla pieces.
Top with shredded cheese, cover, and cook another 10 to 15 minutes until melted.
Top with cilantro and green onions before serving.