Grease the insert of a large 7-quart slow cooker. Add all the ingredients except the chicken. Stir well to combine. Place the raw chicken breasts at the bottom.
Cover with the lid and cook on low heat for 4 hours, or until chicken is cooked through (165°F).
Remove the chicken, shred it on a cutting board, and return it to the slow cooker. Stir to combine.
Serve the soup in individual bowls with your favorite toppings, such as cheese, sour cream, tortilla chips, green onion, and cilantro.
Notes
Customize the toppings to your liking for added flavor and texture. Consider adding tortilla chips for a crunchy element or extra salsa for more spice.