Heat oven to 325°F. In small bowl, combine rosemary, sage, thyme and marjoram. Loosen skin covering turkey breast and pull away, leaving attached at neck. If necessary, use sharp knife to loosen connecting membrane. Rub herb mixture evenly over turkey breast meat. Replace skin over breast, tucking under bottom of breast.
Place turkey breast, skin side up, on rack in roasting pan. Place onion and garlic inside neck opening. Insert meat thermometer so bulb reaches center of thickest part of breast meat, but does not rest on bone. Do not cover or add water.
Bake at 325°F. for 1 3/4 to 2 1/4 hours or until turkey is fork-tender, juices run clear and meat thermometer registers 165 to 170°F. Let stand 10 to 15 minutes before carving. Remove and discard onion and garlic from neck opening.