- Combine soy sauce, horseradish, onion powder, sugar and 1 Tbsp. water; pour over tenderloins in large plastic food storage bag. Press air out of bag; close top securely. Refrigerate 8 hours, or overnight.
- Reserving marinade, place tenderloins on rack in shallow baking pan. Roast at 350ºF. 25 minutes. Turn tenderloins over and brush with reserved marinade. Roast 20 minutes longer, or until meat thermometer inserted into thickest part registers 155º.
- Let stand 5 minutes before slicing.