Remove the giblets and neck from the cavity; freeze or refrigerate for use another time.
Cut the garlic crosswise in half and separate into cloves. Cut the lemon into 1-inch chunks.
Stuff the chicken with the garlic and lemon. Tie the legs together. Twist the wings under the back so the neck skin is pinned in place. Rub the skin with the olive oil and sprinkle with salt and pepper. Place in a roasting pan.
Roast for 1 hour, 15 minutes, checking the temperature with an instant-read thermometer. The chicken is ready when the breast meat registers 160° F and the juice runs clear when the meat is pricked with a fork.
Remove from the oven and let stand 10 minutes. Remove from the roasting pan and pour the pan drippings into a cup. Skim off and discard the fat that comes to the top. Carve the chicken and serve with the pan juices.