Place chicken in slow cooker.
Mix Seasoning Mix, ketchup, hot sauce and brown sugar until blended. Pour over chicken. Cover.
Cook 8 hours on LOW or 4 hours on HIGH. Remove chicken from slow cooker.
Shred chicken, using 2 forks. Return chicken to slow cooker; mix and heat with sauce before serving. Stir in additional hot sauce to taste, if desired. Spoon chicken mixture onto lettuce leaves. Top with shredded carrots, celery sticks and blue cheese dressing. Fold up to enclose filling.