If the turkey is frozen, be sure to completely thaw it. Remove the neck and giblets package from inside and save for gravy or broth, if you like.
Place the turkey on a large cutting board or clean work surface. With a pair of good quality poultry or kitchen shears, cut alongside the backbone, starting at the bottom all the way to the neck of the bird. Then, cut very close to the backbone on the other side to remove the backbone.
Pull the turkey apart where the backbone used to be to reveal the breastbone. At the triangle where the breast bone starts, use shears or a sharp knife to snip into either side of the triangle of cartilage. This will allow the breast bone to open up.
Turn the turkey over and press down on the lower part of the breast to flatten the breast bone. Fold the wings up under the top of the breast.
Pat the bird completely dry with paper towels. Rub the outside skin with olive oil or melted butter.
Combine salt, garlic powder and onion powder; sprinkle over both top and bottom of turkey.
Place a large cooling rack on a foil-lined, rimmed half sheet pan (NOT NONSTICK if going on the grill).
Place the turkey breast side up, on the rack. Flatten the drumsticks by rotating the thighs to be in the center and the drumstick bones on the outside.
Place the turkey, uncovered, in the refrigerator 24 hours and up to 48 hours.