Prep the slow cooker: Lightly coat the insert with cooking spray or a thin layer of oil to prevent sticking.
Mix your sauce base: In a bowl, stir together the enchilada sauce, diced tomatoes with green chiles, chili powder, cumin, smoked paprika, and a pinch of salt and pepper.
Layer the first round: Add a thin layer of the sauce mixture to the bottom.
Scatter a layer of tortilla pieces on top. Add half the onion, half the bell pepper, half the beans, and half the corn. Place the chicken breasts on top (or cooked and crumbled ground meat, or beans if fully vegetarian).
Spoon over more sauce and sprinkle with a third of the cheese.
Repeat layers: Add another layer of tortillas, the remaining onion, bell pepper, beans, and corn. Pour on most of the remaining sauce. Save about 1/2 cup of sauce for the final topping.
Cook: Cover and cook on Low for 5–6 hours or High for 2.5–3.5 hours, until the chicken is tender and easily shreds.
If you used pre-cooked ground meat, you can cook on the shorter end.
Shred the chicken: Remove the chicken to a plate and shred with two forks. Return it to the slow cooker and stir everything gently. If the mixture looks dry, add the reserved sauce and a splash of water or broth.
Taste and adjust seasoning.
Finish with cheese: Sprinkle the remaining cheese evenly over the top. Cover and cook on Low for 15–20 minutes more, until melted and gooey.
Brighten and garnish: Stir in lime juice and cilantro, or sprinkle cilantro over the top. Let the casserole rest for 5–10 minutes to set slightly before scooping.
Serve: Spoon into bowls and add your favorite toppings—sour cream, green onions, avocado, and hot sauce are all great.