Fill a turkey fryer or large stockpot with enough oil to fry turkey, leaving room for oil to rise when turkey is added. Heat oil to 400 degrees F (200 degrees C). Layer a large platter with clean paper bags.
Pat turkey dry with paper towels. Rub seasoning inside cavity and outer surfaces. Make sure hole at the neck is open at least 2 inches so oil can flow freely into cavity.
Turn off heat source. Place onion into the drain basket followed by turkey, neck-end first. Slowly lower the basket into the fryer until turkey is completely submerged in oil. Turn on the heat source and cook, maintaining oil temperature at 350 degrees F (175 degrees C) until no longer pink at bone and juices run clear, about 45 minutes, or 3 1/2 minutes per pound.
Carefully remove the basket from the fryer and drain turkey. An instant-read thermometer inserted into thickest part of thigh, near bone, should read at least 165 degrees F (74 degrees C), but no more than 180 degrees F (80 degrees C). Transfer turkey to the prepared platter to finish draining, 10 to 15 minutes.
