Preheat the oven to 400°F and position the rack in the center.
Make the dry rub by combining all the rub ingredients in a small bowl and whisking them together until well combined.
Spatchcock the chicken by placing it breast side down on a clean cutting surface. Using sharp kitchen shears, cut along both sides of the backbone from the tail end up to the neck and remove it. Discard or freeze the backbone for stock.
Flip the chicken breast side up and press firmly down on the breastbone with the heel of your hand until the chicken flattens. The chicken should lie as flat and even as possible.
Pat the chicken thoroughly dry with paper towels. Carefully loosen the skin over the breasts and thighs with your fingers. Rub a generous portion of the dry rub directly onto the meat under the skin. Lightly brush the skin with oil, then sprinkle the remaining dry rub all over the outside of the chicken, pressing it into the skin to adhere.
Place the chicken skin side up on a rimmed baking sheet or roasting pan. Roast at 400°F for 35-40 minutes.
Remove the chicken from the oven and brush it generously with BBQ sauce. Return to the oven and roast for an additional 10 minutes. Brush with another coat of BBQ sauce and roast for a final 10-15 minutes, or until the internal temperature reaches 165°F in the thickest part of the thigh.
Remove from the oven and allow the chicken to rest for 10 minutes before carving. Serve with additional BBQ sauce on the side.