Preheat oven to 400 degrees F (204 degrees C). Spray a large baking dish or a rimmed baking sheet with cooking spray (line with aluminum foil first for easy clean-up if desired).
Pat pork dry with paper towels and place in prepared dish.
In a small bowl, make a sauce by combining mustard, brown sugar, salt, and pepper. Stir, stir, stir until the sugar basically dissolves into the mustard.
Set aside 3 tablespoons of sauce to use right away. Leave the remaining sauce in the bowl, cover, and set aside to serve with pork later.
Baste about 2-3 tablespoons of the sauce onto the pork.
Wrap bacon around the pork, slightly overlapping each slice and tucking the ends under the tenderloin.
Bake 20 minutes or until cooked to 135 degrees F. Remove from oven and baste with pan juices.
Return pork to oven and bake an additional 10 minutes or until done (about 145 degrees F or 63 degrees C). Keep an eye on your pork because cooking times may vary. I have had slightly larger tenderloins that take a bit more time to cook through.
Tent with foil and allow to rest for at least 5 minutes before slicing. Serve with reserved mustard sauce on the side or baste with the reserved sauce just before slicing.