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.;
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.