in a small bowl, stir together the oil, mustard, Rosemary, and salt. Brush the mixture over the pork. Sprinkle the tenderloins on all sides with the pepper. Cover and refrigerate until ready to cook, up to four hours.
Place the grill rack or broiler pan 4 inches from the heat. Prepare a medium hot charcoal fire or preheat a gas grill for the broiler.
Grill or broil the pork, turning it with tongs so that it is browned on all sides and the meat feels springy when pressed, about 15 to 20 minutes, according to the thickness. The pork should be pink and juicy when cut an instant read thermometer inserted in the center should read 150 to 155°. Do not overcook.
Transfer the pork to cutting board and cover with foil. Temperature will continue to rise 5 to 10° as the meat rest. Let stand about five minutes.
Remove the strengths and carve the pork into 1/2 inch thick diagonal slices. Fan them on a serving platter. Serve warm or at room temperature. Serves 6 to 8