In an 8-inch skillet over medium, toast the Sichuan peppercorns, stirring, until fragrant, about 2 minutes. Transfer to an electric spice grinder and let cool, then pulverize until finely ground. Empty into a large bowl, then stir in the oil, garlic, minced scallions, cilantro stems, lime juice and zest, sugar, 1½ teaspoons salt and ½ teaspoon white pepper. Add the chicken and toss until well coated. Let stand at room temperature while you prepare the grill.

Prepare a charcoal or gas grill. For a charcoal grill, ignite a large chimney of coals, let burn until lightly ashed over, then distribute the coals evenly over one side of the grill bed. Heat the grill, covered, for 5 to 10 minutes, then clean and oil the grate. For a gas grill, turn all burners to high and heat, covered, for 15 minutes, then clean and oil the grate; turn off one burner, leaving the remaining burner(s) on high.

Place the chicken skin side up on the cooler side of the grill. Cover and cook 15 minutes. Using tongs, reposition the chicken so the pieces furthest from the fire are now closest. Re-cover and cook until the thickest part of the breasts (if using) reaches 155°F or the thickest part of the thighs (if using) reaches 175°F, another 5 to 10 minutes. Flip the chicken skin side down onto the hot side of the grill and cook, turning a few times, until well browned on both sides, 4 to 5 minutes. Transfer to a platter and let rest 5 minutes. Sprinkle with the chopped cilantro and sliced scallions; serve with lime wedges.

Oven version: Follow the recipe to make the seasoning mix and apply it to the chicken. Let stand at room temperature while you heat the oven to 450°F with a rack in the middle position. Set a wire rack in a rimmed baking sheet and place the chicken skin side up on the rack. Roast until the skin is crisp and charred in spots and the thickest part of the breasts (if using) reaches 160°F or the thickest part of the thighs (if using) reaches 175°F, about 40 minutes. Transfer to a platter and let rest 5 minutes. Sprinkle with the cilantro leaves and sliced scallions; serve with lime wedges.