Turn the chicken breast side down, with the legs towards you.
Using a sharp knife or a strong pair of kitchen scissors, from the bottom upwards, make a cut to the side of the backbone which you can feel running down the centre of the chicken. Cut all the way to the top, through the bones.
Repeat on the other side, cutting to the side of the backbone all the way to the top.
Remove the backbone completely, cutting through any remaining skin or meat holding it in place, and place it to the side.
Turn the chicken back over and press down to make it even flatter. With the backbone removed the whole chicken will cook through a lot faster.
Make the rub:
Mix the rub ingredients (olive oil and herbs and spices) in a small bowl.