Place the medallions in the baking pan and pour the marinade over them. Place the pan in the oven, uncovered, and roast the medallions for 15 to 20 minutes, or until an instant-read thermometer inserted into the center of the meat reads 140 degrees Fahrenheit.arinated pork medallions roast to a tender, juicy finish in the oven. Purchase pre-marinated pork medallions or make your own marinade to add flavor to the meat.