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 1/4 cup of the marinade mixture and set aside in a small bowl. This will be used for basting during grilling.
03 - Add the chicken thighs and drumsticks to the bowl with the remaining marinade, turning each piece to coat thoroughly. Cover tightly and refrigerate for at least 1 hour, or up to overnight for more intense flavor.
04 - Preheat an outdoor grill to medium-high heat (approximately 375°F to 400°F). Lightly oil the grates using a folded paper towel dipped in vegetable oil to prevent sticking.
05 - Remove the chicken from the marinade, allowing any excess to drip off. Place the pieces skin-side down on the grill and cook for 6 to 8 minutes per side, turning occasionally and brushing with the reserved basting sauce, until the skin is nicely charred and the internal temperature reaches 165°F when measured at the thickest part.
06 - Transfer the chicken to a platter and let rest for 5 minutes to allow juices to redistribute. Garnish with chopped fresh parsley if desired and serve immediately.