Combine all the ingredients in the slow cooker. Stir until combined. Place uncooked chicken on top and cover. Cook on low for 6 hours (this is my ideal way to cook it) or on high for 4 hours, stirring occasionally.
When there is 1 hour left, remove chicken and shred. Stir into sauce and continue cooking. I like to remove the lid about 30 minutes before I serve to cool it off a little and let it thicken
Top with fresh cilantro, shredded cheese, chopped scallions, avocado, sour cream, or plain Greek yogurt.