2. Rinse the chicken inside and out with cold water. Pat dry with paper towels.
3. Drizzle the olive oil over the skin of the chicken. Season the inside and outside of the chicken with salt and pepper. Squeeze the juice from the lemon halves all over the chicken and stuff the lemon halves, thyme, celery and onion into the cavity.
4. Place the chicken on a rack in a roasting pan. Roast the chicken in the oven for 1 to 1 1/2 hours or until a thermometer inserted into the thickest part of the thigh registers 160°F. (Check that the final temperature of the meat is 180°F. The meat will continue to cook after being removed from the oven).
5. Let the chicken rest for 15 minutes. Remove and discard the skin before carving.