Using a food processor or blender, finely chop the onion, chile, garlic, five-spice powder, allspice, thyme and 1 tsp. pepper. With the machine on, gradually blend in the soy sauce, then the oil.
Pat the chicken pieces dry and place in a large bowl; pour the jerk seasoning on top and turn the pieces to coat. Refrigerate for at least 3 hours or up to 24 hours. Remove and let stand at room temperature for 45 minutes before grilling.
Meanwhile, preheat a gas grill to between 350 degrees and 400 degrees . Transfer the chicken to the hot grate, cover the grill and cook, turning once, until the skin is browned and the juices run clear when the joints are pierced with the tip of a sharp knife, about 45 minutes. Remove and let rest for 10 minutes, then, using a sharp knife, split the legs through the joints and serve. Top with the cilantro, if using.