Set a rack at the highest oven position and heat the oven to 400°F
In a small, shallow bowl, whisk the hoisin sauce, vinegar, soy sauce, garlic, and ginger.
Dredge each chicken piece in the glaze, coating completely.
Put the pieces, skin side down, in a rimmed, shallow 10x15-inch sheet pan. Pour any leftover glaze over the chicken; sprinkle liberally with pepper.
Roast on the top rack until the juices run barely clear when you prick the chicken, about 40 minutes.
Remove the pan from the oven and set the broiler on high. Turn the chicken over and baste it with the pan drippings. If a lot of fat has rendered out, spoon some off before broiling to prevent flare-ups.
Broil, basting the chicken and rotating the pan for even browning, until the chicken is shiny and well browned, about 8 minutes.
Drizzle the chicken with the pan drippings before serving.