01 - In a large mixing bowl, combine the barbecue sauce, olive oil, apple cider vinegar, brown sugar, smoked paprika, garlic powder, onion powder, salt, and black pepper. Whisk until smooth and well blended.
02 - Measure out ¼ cup of the marinade mixture and set aside in a small bowl for basting during grilling.
03 - Add the chicken thighs and drumsticks to the remaining marinade, turning each piece to ensure full and even coating. Cover the bowl tightly and refrigerate for at least 1 hour, or up to overnight for more pronounced flavor.
04 - Set your grill to medium-high heat. Lightly oil the grates using a folded paper towel dipped in vegetable oil to prevent the chicken from sticking.
05 - Remove the chicken from the marinade, allowing any excess to drip off. Place the pieces skin-side down on the hot grill. Cook for 6 to 8 minutes per side, turning occasionally and brushing with the reserved basting sauce, until the skin is deeply charred and an instant-read thermometer inserted into the thickest part registers 165°F (74°C).
06 - Transfer the chicken to a platter and let it rest for 5 minutes to allow the juices to redistribute. Garnish with chopped fresh parsley if desired and serve immediately.