1. Combine the lemon zest, rosemary, minced garlic, salt and pepper to create a paste. Set aside.
2. Butterfly the chicken: Lay the chicken breast side down so the tail faces you. Using kitchen or poultry shears, cut along one side of the backbone. Turn the chicken so the neck is facing you, keeping the breast side down. Cut along the backbone along the other side. Remove the backbone.
3. Flip the chicken so the breast side is up. Spread the sides to open the chicken. Push down with your hands to flatten the chicken and break the breast bone. Make half-inch slits on either side of the breast, about 1-inch from the end and tuck the wing tips into the slits.
4. Use the smooth face of a kitchen mallet and pound the chicken to even the thickness. This will ensure that the chicken will cook evenly.
5. Loosen the skin on each leg and thigh. Rub 1/2 of the lemon-rosemary paste under the skin of the two legs and thighs. Loosen the skin on the breast and rub the remaining paste under the skin.
6. Transfer the prepared chicken to a broiler pan, skin side up. Brush with oil and lightly season with salt and pepper.
7. Preheat the broiler and adjust the rack so the chicken is no closer than 8-inches to the heating element or flame.
8. Broil the chicken until the skin is a rich, dark brown – about 12-minutes. Flip the chicken and continue to broil until the juices run clear – about 15 minutes.
9. Remove the chicken from the oven. Flip it again, so the skin is on top. Brush the skin with the pan drippings and return to the broiler. Broil until the skin is crisped – about 3-minutes.
10. Remove from the oven and cover with foil. Let rest 10-12 minutes before carving.