Set the chicken on a cutting board, breast-side-down. With kitchen scissors or a knife, cut along either side of the chicken’s backbone and remove. (The backbone is directly opposite the breast). Set the chicken, breast-side-up, and firmly press it flat, and then set in large, sided dish.
In a small bowl, combine the remaining ingredients, except salt and pepper. Brush this mixture all over the chicken. Cover, refrigerate and marinate chicken 4 hours, turning occasionally.
Preheat your barbecue to 375°F. Season the chicken with salt and pepper. Place the chicken, breast-side-up, on one side the barbecue. Close the lid and turn the heat off underneath the chicken; leave the other side of the barbecue on. Cook the chicken 45 to 50 minutes, or until the temperature in the deepest part of the thigh registers 170°F on an instant-read meat thermometer. (As the chicken cooks, check the temperature in the chamber and ensure it stays around 375°F, adjusting the flame as needed.)
If desired, once cooked, for added colour move the chicken to the lit side of the barbecue and grill a minute or so on either side to lightly char. Transfer the chicken to a large plate and rest 5 minutes before cutting into portions. If desired, for even more flavour, just before serving drizzle the chicken with a little olive oil and lemon juice.