Directions: Trim the tenderloin of excess fat. Rub the Cajun seasoning and olive oil onto the tenderloin. Heat a large saut, pan until very hot. Brown the tenderloin on all sides for approximately 2 minutes. Place the browned meat onto a roasting rack inside a shallow baking pan. Rub the top and sides of the meat with the Dijon mustard. In a small bowl, combine the horseradish, garlic, salt, and pepper. Press the mixture onto the top and sides of the meat, over the mustard. Roast the tenderloin, uncovered, at 400 degrees for 35 minutes for medium rare. Let the roast rest for 5 minutes before slicing.