Combine the onion, scallions, chiles, garlic, five-spice powder, allspice, pepper, thyme, nutmeg, and salt in a food processor and process to a coarse paste. While the machine is running, slowly drizzle in the soy sauce and oil. Pour the marinade into a large, shallow dish, add the chicken, and coat well. Refrigerate overnight, covered. Allow the chicken to come to room temperature before continuing.

Start a grill. Grill the chicken over a medium-hot fire, turning occasionally, for 35 to 40 minutes, or until well browned and cooked through. (For a smokier flavor, cover the grill.) Place the chicken on a serving platter and serve.