Preheat your grill until it reaches around 375-400 degrees.
On a platter or cutting board, lay out 4 pieces of bacon parallel to each other and on an angle. Place the pork tenderloin down the center of the bacon. Salt and pepper the tenderloin.
Spread the dijon mustard down the length of the tenderloin, slightly down the sides. Sprinkle the brown sugar on top of the mustard, pressing it in lightly with your fingers. Sprinkle the chopped flat leaf parsley on top of the brown sugar.
Take each end of the bacon and wrap the tenderloin, one by one. Secure the ends with toothpicks.
Place the bacon wrapped tenderloin over the direct heat of the grill. Rotate the tenderloin every 3 minutes until the bacon is slightly crisp then either turn down the heat or move it to the indirect heat of the grill. Continue to grill until internal temp reaches 140-145 degrees. This should take 20-25 minutes depending on the thickness of your pork. Watch it closely so that the bacon does not burn too much.
Remove from grill and let it rest, covered with foil, for about 5-10 minutes so the juices redistribute. Remove toothpicks and slice and serve.