In a large mixing bowl add the butter, lemon juice, lemon zest, sage, rosemary and thyme. Salt and pepper to taste. Mix thoroughly and refrigerate.
Place the turkey breast down on a cutting board and use a knife or kitchen shears to cut along each side of the backbone and remove it. Flip the turkey over and press down on the breast to flatten it. Trim off any excess skin.
Run your fingers between the skin and meat to separate them. Rub the lemon herb butter directly on the meat and press down on the skin. Rub the remaining mixture on the outside of the skin.
Wrap the turkey in clear plastic wrap and place in an aluminum roasting pan. Place on top of ice in a cooler.
Set up the grill for indirect cooking and heat to 325-350°F. Place a drip pan below the cooking grate.
Remove the clear plastic wrap from the turkey and place it skin side up on the cooking grate.
Roast for 90 minutes or until the breast reaches an internal temperature of 160°F.
Remove the turkey from the grill and wrap loosely with aluminum foil. Rest for 20-30 minutes.
Cut off the legs, thighs and wings and set aside. Carve the breast meat and serve.