Pour the barbecue sauce directly into the crockpot, followed by the Italian dressing, brown sugar, and Worcestershire sauce. Add the garlic powder, black pepper, and red pepper flakes if using. Whisk everything together thoroughly inside the crockpot until the sauce is smooth and fully combined. Mixing the sauce directly in the crockpot reduces dishes and ensures even flavor.
Place the thawed chicken breasts directly into the prepared sauce. Turn the chicken slightly to ensure each piece is fully coated. The chicken should sit submerged or mostly covered in the sauce for best results.
Cover the crockpot with the lid and cook on high for 4 to 6 hours, or until the chicken is fully cooked and very tender. The chicken should easily pull apart with minimal effort once done.
Using two forks, shred the chicken directly inside the crockpot without removing it. The chicken will be soft and easy to shred due to the long cooking time in the sauce.
After shredding, allow the chicken to sit in the sauce for 15 to 20 minutes with the crockpot still on. This resting time allows the meat to absorb the sauce and helps the mixture thicken slightly.
Serve the pulled BBQ chicken on sturdy, crusty rolls or fluffy sandwich buns that can hold the sauce well. This dish pairs well with chips or coleslaw for a simple, complete meal.