Preheat oven to 425°.
To prepare stuffing, heat a large skillet coated with cooking spray over medium heat. Add onion, celery, and garlic; cook 7 minutes or until tender, stirring frequently. Remove from heat. Stir in dried plums and next 8 ingredients (dried plums through 1/4 teaspoon pepper); set aside.
Slice pork lengthwise, cutting to, but not through, other side. Open halves, laying pork flat. Place plastic wrap over pork; pound to 1/2-inch thickness using a meat mallet or rolling pin.
Spread stuffing over pork, leaving a 1-inch border. Roll up tightly; secure at 1 1/2-inch intervals with twine. Rub pork with 1/4 teaspoon salt and 1/4 teaspoon pepper. Place pork on a rack in a broiler pan coated with cooking spray. Bake at 425° for 40 minutes or until a meat thermometer inserted in center of pork registers 155°, turning the pork after 20 minutes. Place pork on a cutting board; let stand 10 minutes. Cut into thin slices.
To prepare sauce, whisk together the flour and 1/4 cup broth. Place roasting pan over medium heat. Add port, stirring to loosen browned bits. Whisk in flour mixture, mustard, and 1 1/4 cups broth. Cook 2 minutes or until slightly thick, stirring frequently with a whisk. Stir in 1/4 teaspoon salt and 1/8 teaspoon pepper. Serve with pork. Garnish with parsley, if desired.
MyRecipes is working with Let's Move!, the Partnership for a Healthier America, and USDA's MyPlate to give anyone looking for healthier options access to a trove of recipes that will help them create healthy, tasty plates. For more information about creating a healthy plate, visit www.choosemyplate.gov.