01 - Preheat the oven to 400°F (204°C) or heat a grill to medium-high.
02 - In a bowl, whisk together ketchup, apple cider vinegar, brown sugar, Worcestershire sauce, Dijon mustard, smoked paprika, garlic powder, onion powder, black pepper, and salt until smooth.
03 - Arrange chicken pieces and onion slices evenly in a large roasting pan or on a grill-safe tray.
04 - Generously brush the chicken and onions with half of the BBQ sauce, coating all sides.
05 - Place the chicken in the oven or on the grill. Cook for 25 minutes, turning pieces once halfway through.
06 - Brush the chicken with the remaining BBQ sauce. Roast or grill for an additional 10–15 minutes, or until the chicken is cooked through and the sauce is bubbling and caramelized.
07 - Remove the chicken from the heat and let rest for 5 minutes before serving.