SET UP: Prepare an outdoor grill so that you have a medium-hot fire for both direct and indirect grilling (move hot coals to just one side of the grill, or turn on only half the burners on a gas grill). Once hot, brush the grill grates with oil.
GRILL THE CHICKEN: Pat the chicken dry and sprinkle with 1 teaspoon salt and a couple turns of pepper. Grill the chicken, skin-side up, over direct heat (the hotter side) until lightly charred, about 4 minutes. Flip and cook until faint grill marks appear on the skin, 3 to 5 minutes more. Flip again and move the chicken to the indirect side of the grill (the cooler side). Cover and cook until an instant-read thermometer inserted into the thigh registers 165 degrees F, about 40 minutes.
MAKE THE BBQ SAUCE: Meanwhile, heat the 2 tablespoons oil in a medium saucepan over medium-high heat. Add the onion and cook, stirring occasionally, until softened, about 8 minutes. Add the chile powder and cook, stirring, for about 1 minute. Add the ketchup, peach preserves, and 1/2 cup water and bring to a simmer. Simmer until slightly thickened, about 8 minutes. Add the pickles. Puree with an immersion blender or transfer to a blender. Set aside 1 cup of the sauce for serving.
BASTE AND SERVE: When the chicken is just fully cooked, begin basting it with some of the remaining BBQ sauce and move it back to direct heat. Continue to baste it, gently flipping often, until glazed and lightly charred, about 5 minutes. Serve with the reserved BBQ sauce on the side.
Recipes from "The Chopped Cookbook: Use What you've Got to Cook Something Great" (c) Copyright 2014 by Television Food Network, G.P. By arrangement with Clarkson Potter/Publishers.