Remove giblets and neck from turkey and reserve for broth. Rinse turkey with cold running water and pat dry with paper towels. Place onion and lemon quarters in neck and body cavities.
In a small bowl, mix oil with herbs, salt and pepper. With your finger tips, gently loosen skin from the breast without pulling off the skin. Place 1 tablespoon of herb mixture under skin; replace skin. Rub cavities and outside of turkey with remaining herb mixture.
Secure the neck skin to the back with skewers. Fold wings under back of turkey. Place legs in tucked position. May be prepared to this point, covered and refrigerated for several hours.
Place turkey, breast side up, on a rack in a large shallow (no more than 2-1/2 inches) deep roasting pan. Insert an oven-safe thermometer into the thickest part of the thigh, being careful it does not touch the bone.
Cover bird with a loose tent of foil. Roast turkey in a preheated 325 degree F. oven for about 2-1/2 hours. Remove foil and baste bird with pan juices. Continue to roast for about another hour until meat thermometer registers 180 degrees F. in the thigh.
Remove turkey from oven and allow to rest for 15-20 minutes before carving. Transfer to a large platter and serve with gravy. Note: Yields 18 servings at 6 ounces per portion.