Preheat oven to 200°C/390°F.
In a ceramic or glass baking dish, whisk together ketchup, apple cider vinegar, Worcestershire sauce, brown sugar, mustard powder, onion powder, salt, pepper, and water.
Add the chicken and coat well in the barbecue sauce. Arrange chicken skin-side down.
Bake for 20 minutes.
Remove from oven, turn the chicken over, and spoon sauce generously over each piece.
Return to oven and bake for another 30 minutes.
Remove the pan again and spoon more sauce over the Oven Baked BBQ Chicken.
Optional: skim excess fat from the pan using a spoon.
Switch oven to broil/grill on high. Broil chicken for 2–3 minutes until the sauce thickens and caramelizes beautifully.
Garnish with parsley or green onions before serving.