In a slow cooker, stir together the tomatoes, green chilis, and taco seasoning. Place the chicken breast on top of the tomato mixture and cook on low heat in the slow cooker for 1 1/2 to 2 hours, or until the chicken reaches an internal temperature of 165 degrees. If your chicken breast is especially thick, it may take up to 3 hours. Keep an eye on the temperature with a meat thermometer.
Once it's cooked through, use two forks to shred the chicken in the slow cooker. (You could also remove the chicken to a cutting board and shred it there. Then return it to the slow cooker.) Stir in the refried beans, and cook on low for another 10 minutes. Taste the mixture, then add a little salt or taco seasoning if needed. I tend to add a little salt, but you may not need it if your canned tomatoes have salt in them.
Preheat the oven to 250 degrees. Wrap the stack of tortillas in aluminum foil and place them in the oven. Once they’re warm, remove them from the oven. Place a piece of lettuce on each tortilla, then spread 1/2 cup of the warm chicken mixture on the lettuce. Top with cherry tomatoes, avocado, corn, and cilantro (or whatever taco toppings you’d like). Serve immediately.