01 - Set oven temperature to 350°F.
02 - Combine butter, garlic, parsley, sage, rosemary, thyme, lemon zest, salt, and pepper in a small bowl until fully integrated.
03 - Dry the turkey breast with paper towels. Gently separate skin from meat using fingers. Spread half of the herb butter beneath the skin, and rub the remainder over the exterior surface.
04 - Place lemon and onion slices in a roasting pan. Position the turkey breast skin-side up on top. Pour chicken broth or water into the pan.
05 - Cook uncovered for 60 to 75 minutes, or until internal temperature reaches 165°F at the thickest point. Baste with pan juices halfway through. Cover loosely with foil if skin browns prematurely.
06 - Remove from oven and let rest for 15 minutes before slicing. Serve with pan juices.