How to Make It
In a small skillet, toast the Szechwan and black peppercorns over moderate heat until fragrant, about 1 minute. Transfer to a bowl and let cool.
In a spice grinder, grind the peppercorns. Transfer to a bowl and mix with the salt, ginger, garlic and sesame oil until a coarse paste forms. Spread half of the paste under the chicken's skin and rub the remaining paste all over the skin. Tie the chicken's legs together with kitchen string.
Light a grill and set it up for indirect grilling. If using charcoal, when the fire is medium hot, rake the coals into two piles on opposite sides of the grill. Place a foil drip pan in the center of the grill. If using a gas grill, light the front and rear or outside burners.
Lightly brush the grate with vegetable oil. Set the chicken on the grill, breast side up, over the drip pan, away from the heat. Cover and grill until the skin is crisp and an instant-read thermometer inserted into the inner thigh registers 165°, about 1 1/2 hours. Transfer to a cutting board and let stand for 5 minutes before carving. Serve with the Hoisin Barbecue Sauce and the grilled scallions and onions.