1. In a large stockpot or turkey fryer, heat oil to 400 degrees F (200 degrees C). Be sure to leave room for the turkey, or the oil will spill over. Layer a large platter with food-safe paper bags.
2. Rinse turkey, and thoroughly pat dry with paper towels. Rub Creole seasoning over turkey inside and out. Make sure the hole at the neck is open at least 2 inches so the oil can flow freely through the bird.
3. Place the whole onion and turkey in drain basket. The turkey should be placed in basket neck end first. Slowly lower basket into hot oil to completely cover turkey. Maintain the temperature of the oil at 350 degrees F (175 degrees C), and cook turkey for 3 1/2 minutes per pound, about 45 minutes.
4. Carefully remove basket from oil, and drain turkey. Insert a meat thermometer into the thickest part of the thigh; the internal temperature must be 180 degrees F (80 degrees C). Finish draining turkey on the prepared platter.