Combine all of the marinade ingredients in a small bowl, stirring until sugar dissolves.
Put teriyaki marinade and pork in a sealable plastic zip bag. Seal the bag and marinate the pork in the refrigerator, turning once, for at least 30 minutes or up to 4 hours.
Preheat the broiler. Remove the pork from the marinade and discard the marinade. Place pork on roasting pan and broil until an instant-read meat thermometer inserted into the thickest part registers 145℉, about 15 minutes, turning once. Let rest for 10 minutes before slicing. Alternately, you can roast it in the oven. Bake for 20 minutes in 400℉ oven.
Notes
If you'd like to make an additional teriyaki sauce for spooning over the cooked pork tenderloin, just double the ingredients in the marinade. Use half for the marinade, and simmer the other half in a pan on the stove until slightly thickened.
If you are preparing this recipe as GLUTEN FREE, just be sure to use a brand of soy sauce that is known to be GF.