1) Preheat oven to 200C/Gas 6. Coat a large roasting pan with cooking spray.
2) 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.
3) Roast for 30 minutes, or until an instant-read thermometer registers at least 71C. Remove from oven and let pork rest for 10 minutes. Cut crosswise into 1/2cm-thick slices.
4) 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 10-15 minutes. Remove from heat.
5) Toss somen noodles with spring onions and groundnut oil.
6) Remove pork from the oven. Serve two thirds of the pork with all of the plum sauce and somen noodles. Reserve remaining pork, about 12-16 thin slices, for paninis.