Arrange chicken pieces in a baking dish in a flat layer.
Stir ketchup, bell pepper, onion, water, oil, vinegar, salt, garlic powder, and black pepper together in a bowl; pour evenly over chicken pieces to coat.
Bake the chicken, basting occasionally, in the preheated oven until no longer pink at the bone and the juices run clear, about 2 hours. An instant-read thermometer inserted into the thickest part of the thigh, near the bone should read 165 degrees F (74 degrees C).