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 it aside for basting during grilling. Keep it covered at room temperature.
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 your grill to medium-high heat (approximately 375°F to 400°F). Lightly oil the grates 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. Cook for 6 to 8 minutes per side, brushing with the reserved marinade and turning occasionally, until the skin is nicely charred and the internal temperature reaches 165°F.
06 - Transfer the chicken to a platter and let it rest for 5 minutes. Garnish with chopped fresh parsley if desired and serve immediately.