Whisk together honey, mustard, vinegar, thyme, and pepper. Place pork tenderloin in a large zip-top bag and pour in honey mustard mixture. Squish around to make sure pork is completely covered. Refrigerate at least one hour.
Heat oven to 425F. Oil the baking dish lightly
Place pork on the dish, reserving the marinade. Roast it from 35 minutes to an hour, depending on the thickness of tenderloin. Check internal temperature at 30 minutes. Pork is done when a thermometer inserted into the center reads 145F. Remove from oven and leave alone for 10 minutes before slicing.
Place reserved marinade in small saucepan and boil for 5 to 10 minutes or until thickened. Add water ass needed to prevent sticking.
Serve pork and drizzle with the honey mustard sauce.