Whisk together ketchup, vinegar, brown sugar, molasses, Worcestershire sauce, mustard, garlic powder, onion powder, pepper and ¼ cup water. Reserve ⅓ cup of marinade and set aside.
Combine ketchup mixture and chicken in an extra-large slider bag or large bowl; marinate for at least 1 hour to overnight, turning the bag occasionally. Drain the chicken from the marinade.
Preheat grill to medium-high heat.
Make drainage holes in a sheet of ALCAN® Non-Stick Baking Foil with a grilling fork. Place foil sheet on grill grate with non-stick (dull) side facing up. Immediately place chicken on foil.
Add chicken to grill and cook, flipping once and basting with reserved ⅓ cup marinade until cooked through, about 10-12 minutes on each side.
Serve immediately, garnished with parsley, if desired.