To butterfly chicken: place chicken, breast-side down, onto a clean board and, using poultry shears or kitchen scissors, on one side of the back bone cut along the entire length of the back bone, as close to the bone as possible.
Open chicken out as much as possible and place onto a flat surface with the skin side up.
To flatten the chicken: using the heel of your hand press firmly on the breastbone breaking the breast bone, collar bones, rib cage and wishbone.
Into a large bowl add salt and pour over water. Stir to dissolve salt.
Place chicken into brine and completely submerge. Top with a plate to keep chicken submerged. Refrigerate for 24 hours.
Remove chicken from brine and pat dry using paper towels.
Cut wing tips off at the first joint. Remove backbone by cutting out with poultry shears or kitchen scissors.
Starting from the neck end, and working over one breast at a time, loosen skin by sliding your fingers between the skin and flesh. Work slowly and gently down towards the leg. Leave skin attached only at the tip of the drumstick.
Into a small bowl place garlic and rosemary and mix with a fork to make a paste. Using your fingers rub paste between chicken flesh and skin.
Position Caramelized Lemon Slices under skin sitting three slices on each breast and two down each leg.
Rub outside of chicken with olive oil and sprinkle with pepper. Refrigerate for up to one day or barbecue immediately.
Preheat barbecue char grill or flat plate to medium-high.
Place chicken, skin-side down, onto the preheated barbecue and cook for 12 minutes till skin is dark golden.
Using a firm spatula turn chicken over and cook for 15 minutes.
Turn barbecue down to its lowest setting and cover chicken with an upturned deep roasting tray, or place barbecue lid over the chicken.
Cook for a further 15 minutes or till chicken juices run clear.
Remove chicken from barbecue and leave to rest for 10-15 minutes, away from the heat, in a roasting tray covered with aluminium foil.
Chop into 8- 10 portions and serve immediately.