With kitchen shears or a knife, cut along both sides of the backbone and remove it. Open the carcass and cut longitudinally into the breast bone. Place the opened chicken onto the counter, cavity side down, and press to crack the breast bone and create a spatchcocked chicken.
Heat one side of the grill.
Rub the chicken with 2-3 Tbs of spice and some extra salt and pepper.
Place the chicken on the cool side of the grill open side down and cook until a meat thermometer placed in the thigh reads 155°F. It will take about 45 minutes for a 3# bird and 60 minutes for a 4# bird.
Flip the chicken, skin side down, onto the hot side of the grill and cook for 10 minutes.