1. In a medium bowl, whisk soy sauce and sugar until the sugar is completely dissolved; stir in garlic, ginger, chile and oil.
2. Place pork in a heavy duty, resealable plastic bag and add marinade; squeeze air out and seal. Turn the bag to coat the medallions, then refrigerate for 2 hours, turning the bag once to redistribute the marinade. (I marinated several hours, turning at least every couple of hours.).
3. Preheat grill to medium. Remove pork from marinade (discard marinade); grill until just cooked through, 3 to 5 minutes per side.
4. *Note: I've seen several questions and a bit of confusion in the forums here regarding pork tenderloin versus pork loin roast. They are not the same. Pork tenderloin is a very lean, tender cut from the loin section. It is long and slender, and usually weighs between 3/4 and 1 1/2 pounds. It has a mild flavor, so it benefits from being prepared with a rub, marinade or sauce, but does NOT benefit from extended cooking. To keep tenderloin juicy, make sure you don't overcook it. Contrary to rules from the past, most pork now is safe and best enjoyed still slightly pink in the center ;).