Adjust an oven rack to the middle position and preheat the oven to 450°. Line a rimmed baking sheet or broiler pan with tin foil.
Scatter the chopped veggies and thyme sprigs across the bottom of the pan. Place a wire rack on top of the vegetables
Pat the turkey dry with paper towels. Loosen the turkey skin from the breasts and rub the turkey all over and under the skin with 1 tablespoon of the oil. Season liberally all over with salt and pepper (go easy on the salt if the bird was dry brined. Tuck the wings under the bird, place it on the rack (be sure that it doesn't hang over the edge of the pan) and press down firmly on the breastbone to flatten the breasts slightly.
Roast, rotating the pan occasionally, until an instant - read thermometer inserted into the deepest. part of the breast registers 150° and the thighs register at least 165°, about 80 minutes. (I had an 18 pound turkey and I cooked it for 108 minutes), so figure about 6 minutes per pound. If the vegetables start to burn or smoke, add 1 cup of water or broth to the roasting pan.
Once the turkey has reached the above temperatures, remove from the oven and tent the turkey with aluminum foil and allow it to rest at room temperature for 20 minutes before carving,
Pour any collected juices from the roasting pan or baking sheet through a fine mesh strainer and use for your gravy base.
Carve the turkey and enjoy!