Toss potatoes in oil and salt and pepper in a large plastic resealable bag. Remove potatoes from bag; set potatoes aside. Save the bag for the pork tenderloin.
Mix jelly and mustard in small bowl. Place jelly mixture in plastic bag with pork tenderloin. Mix well to coat all sides.
Preheat contact roaster. Place tenderloin directly in contact roaster, add potatoes. Set timer and cook, covered, 10 minutes. Turn tenderloin over and brush with remaining jelly mixture. Cook covered 10 more minutes.
Remove tenderloin and potatoes from roaster; cover with foil and rest 10 minutes before slicing. Serve with fingerling potatoes.