Prepare the slow cooker with nonstick cooking spray. Place the chicken breasts or thighs in the slow cooker. Sprinkle or pour the remaining ingredients over the chicken.
Cover the slow cooker and cook on the low setting for 4 to 6 hours or until the chicken is tender and easily shreds with two forks.
Once the chicken is cooked, use two forks to shred it directly in the slow cooker. Stir into the sauce, allowing it to absorb the flavors
Serve it inside warmed small tortillas with chopped cilantro, sour cream, slices of avocado and cheese.