Here's how it's done: Using a sharp knife or, better still, kitchen shears, cut out the bird's backbone. Discard. Spread out the bird, and press down on it with your palms until as flat as possible. The larger the bird, the more athletic this process will be. Mark Bittman's video, which inspired me to move beyond quail and such, makes the process look as easy as it is.
I coated the 3 1/2 pound chicken in olive oil, Middle Easter spices (za'atar), and salt. (Use any spice/fat blend you like, even just oil/butter, salt, and pepper.) I greased a pan and roasting rack (not essential), then roasted the spatchcocked (I just love saying that) bird for 15 minutes at 425, 15 at 350. The result was crisp skin, juicy meat, and a perfect thigh temp of 160. Your mileage may, of course, vary. Use a meat thermometer to check for doneness!