Place the chicken breasts in the bottom of the slow cooker in a single layer.
In a mixing bowl, whisk together the BBQ sauce, Zesty Italian dressing, brown sugar, and Worcestershire sauce until smooth and combined.
Pour the sauce mixture evenly over the chicken, covering each piece.
Cover and cook on low for 4–6 hours or on high for about 3 hours, until the chicken is cooked through and tender.
Use two forks to shred the chicken directly in the slow cooker and stir to combine with the sauce.
Serve warm, for example on hamburger buns or as desired.