Add chopped onion to the bottom of a slow cooker. Rub chicken in ranch seasoning and place on top of onion.
Mix BBQ sauce and hot sauce and pour over chicken. Slow cook on low for 6-7 hours or until chicken easily shreds with a fork.
Remove chicken from slow cooker, shred with two forks, then return to slow cooker and mix chicken with juices.
Serve chicken on top of lettuce leaves with julienned celery and carrots. Add additional hot sauce just before serving, if desired. Top with guacamole or ranch dressing, if desired, and garnish with chives.