Place chicken breasts in the bottom of your slow cooker, arranging them in a single layer if possible.

In a medium bowl, whisk together ketchup, brown sugar, apple cider vinegar, Worcestershire sauce, and yellow mustard until well combined.

Add garlic powder, onion powder, smoked paprika, black pepper, salt, and cayenne pepper to the sauce mixture, whisking until all spices are fully incorporated.

Pour the BBQ sauce mixture over the chicken, ensuring all pieces are well coated.

Cover and cook on LOW for 6-7 hours or HIGH for 3-4 hours, until chicken is tender and easily shreds with a fork.

Remove chicken from slow cooker and place on a cutting board or large plate.

Using two forks, shred the chicken into bite-sized pieces, removing any visible fat or connective tissue.

Return shredded chicken to the slow cooker and mix with the remaining sauce.

Let it sit for 10-15 minutes to absorb the flavors before serving.

Taste and adjust seasoning if needed, adding more salt, pepper, or hot sauce as desired.