Season pork all over with salt and black pepper and place in prepared pan. In a small bowl, whisk together soy sauce, molasses, hot mustard, and garlic powder. Brush soy sauce mixture all over pork. Roast for 30 minutes, or until an instant-read thermometer registers at least 160 degrees F. Remove from oven and let pork rest for 10 minutes. Cut crosswise into 1/4-inch thick slices.;
For the sauce:
While the pork is roasting, in a small saucepan, combine plum preserves, chutney, vinegar, sugar, and ginger. Set pan over medium heat and bring to a simmer for about 10 to 15 minutes. Remove from heat.
Toss somen noodles with scallions and peanut oil.
Remove pork from the oven. Serve 2/3 of the pork with all of the plum sauce and somen noodles. Reserve remaining pork, about 12 to 16 thin slices, for paninis.