Honey-Glazed Pepper Chicken

Finely grind black peppercorns and 2 Tbsp. pink peppercorns in a spice mill or mortar and pestle. Transfer to a small bowl and mix in 5 tsp. Diamond Crystal or 2¾ tsp. Morton kosher salt; set seasoning aside.
Place chicken, breast side down, on a cutting board and use kitchen shears to cut along both sides of the backbone to remove (freeze and save it for stock!). Open chicken and turn skin side up. Press down on center of breast to flatten chicken—you should hear the breastbone crack. Using a chef’s knife or cleaver, split chicken in half through breastbone. Pat dry; rub all over with 1 Tbsp. oil. Sprinkle reserved seasoning all over, making sure to get into all the nooks and crannies. Place on a wire rack set inside a rimmed baking sheet. Chill, uncovered, at least 8 hours and up to 2 days.
Coarsely grind remaining 2 Tbsp. pink peppercorns in spice mill or mortar and pestle. Cook chiles, honey, vinegar, and remaining 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt over medium heat, stirring occasionally, until mixture just turns amber in color and is reduced by about half (it should coat a spoon), 10–12 minutes. Stir in pink pepper and set aside.
Prepare a grill for medium heat. Lightly oil grate. Set chicken on grate, cover, positioning vent over chicken if your grill has one, and grill, turning every 5 minutes, until an instant-read thermometer inserted into the thickest part of thighs registers 120°–130°F, 15–20 minutes. Continue to grill, basting with honey mixture and turning chicken every 2–3 minutes, until an instant-read thermometer inserted into the thickest part of thighs registers 175°F and 155°F in the thickest part of breast, 10–15 minutes longer. Transfer to a cutting board and place skin side up. Let rest 30 minutes before carving.