Place the fully thawed chicken breasts in the slow cooker; thaw frozen chicken in the refrigerator before starting.

Mix BBQ sauce, honey, and Worcestershire in a bowl; pour over chicken.

Add sliced onion, if using.

Cover; cook on low 6 hours or high 4 hours until thickest piece reaches 165°F.

Shred chicken with two forks in cooker; stir to coat and serve on buns, over rice, or with favorite sides.