In a small skillet, fully cook chorizo over medium heat, breaking meat into crumbles, 6-8 minutes; drain. Transfer to a 3- or 4-qt. slow cooker. Add next 9 ingredients; stir to combine. Cook, covered, on low until chicken is tender, 4-5 hours., Remove chicken; cool slightly. Shred with 2 forks. Remove and discard onions; strain cooking juices and skim fat. Return cooking juices and chicken to slow cooker; heat through. Serve chicken in corn tortillas. If desired, top with shredded lettuce and pico de gallo., Freeze option: Freeze cooled chicken mixture in freezer containers. To use, partially thaw in refrigerator overnight. Heat through in a saucepan, stirring occasionally; add broth if necessary.