Wash the chicken and pat dry inside and out with paper towels. Combine Szechwan peppercorns, salt, and fivespice powder in a small bowl. Rub the seasonings into the outside and inside cavity of the bird. Place the chicken in a large bowl, cover, and refrigerate 8 hours or overnight.
Fill the lower part of a steamer with enough water to come within an inch of the cooking rack. Bring the water to a rolling boil, place the chicken on the rack, and cover the steamer. Steam the chicken for 45 minutes, keeping the water at a boil and replenishing it as it boils away.
Line a large wok or a heavy Dutch oven with tightfitting lid with heavyduty aluminum foil.
Combine the smoking mixture ingredients and spread over the foil in the bottom of the pot. Turn the heat under the pot to high and place a rack about 3 inches above the smoking mixture so that the chicken does not touch it. Place the chicken on the rack, breast side up. Line the inside of the lid with more foil, leaving an excess of 3 inches around the lid. Cover the pot tightly and crimp the foil down so the lid fits securely and smoke doesn't escape.
After you detect smoke, smoke the chicken for 20 to 25 minutes. Turn off the heat and let the smoke subside, about 5 minutes. The chicken should be a rich, golden brown on the outside.
Lift out the smoked chicken and transfer to a cutting board. Immediately brush the sesame oil lightly over the outside. Allow chicken to cool, about 10 minutes. To serve, cut off the wings and legs. Divide the body of the chicken in half lengthwise by cutting through the breast and backbone. Lay the halves flat on the cutting board, skinside up, and use a cleaver to chop through each half, bones and all, into 3 to 4 equal pieces. Chop the wings and legs into pieces as well. Arrange the chicken pieces on a large platter, and garnish with the scallion brushes.