Preheat oven to 325 degrees.

In a small bowl, mix the olive oil, garlic, rosemary, basil, Italian seasoning, black pepper and salt; set aside.

Wash the turkey inside and out; pat dry with paper towels. Remove any large fat deposits. Loosen the skin from the breast by slowly working your fingers between the breast and the skin, being careful not to tear the skin.

Using your hand, spread a generous amount of the rosemary and olive oil mixture under the skin. Rub the remainder of the rosemary mixture over the outside of the breast. Use toothpicks to seal skin over any exposed breast meat.

Place the turkey, breast side down, on a rack in a roasting pan.

Place the quartered onion pieces (as many as you can fit) inside the breast cavity.

Add about 1/4 inch of water to the bottom of the pan.

Roast in the preheated oven for approximately 3 hours, or until the internal temperature of the bird reaches 165 degrees.

If desired, turn the turkey breast over with about an hour left of cooking time to allow the top to brown. Let sit for 15-20 minutes before carving.