Mist a slow cooker with cooking spray. Season chicken with salt and pepper and place in slow cooker. In a large bowl, mix remaining ingredients except for optional rice or tortillas. Pour over chicken; turn to coat. Cover and cook on low until chicken is falling-apart tender, 3 to 5 hours.
Turn slow cooker to warm and, using two forks, shred chicken. Serve over rice or with warmed tortillas, if desired.