Place chicken, and the remaining ingredients except the toppings in the bowl of a slow cooker. Cook on high for 3-4 hours. Stir every hour to combine the flavors.
After 3 hours check if the chicken will separate easily with a fork and then it is done. When done, transfer the chicken to a cutting board, and shred using two forks.
Return to the cooker, and mix in with the juices. Serve on four tortillas with avocado, red cabbage, crumbled cotija, and lime wedges.