Place the chicken breasts and chopped onions into the bottom of a slow cooker.
Min a medium bowl, whisk together the barbecue sauce, honey, Worcestershire sauce, and olive oil. Pour over the chicken.
Cover and cook for 6 hours on LOW or 3 hours on HIGH.
When there are 30 minutes left of cooking time, uncover and shred the chicken using 2 forks right in the slow cooker. Then mix the chicken back into the sauce. Cover and continue cooking for 30 minutes.