For the pork roast: Preheat the oven to 350°F/180°C Place a large sauté pan over high heat. Season the pork loin with salt and pepper. Drizzle 1 tablespoon/15 ml of oil over the pork and rub to coat the pork all over with the oil.
Cook the pork in the hot pan until golden brown on all sides, about 8 minutes total. The pork will still be raw. Place the sauté pan in the oven and roast the pork for approximately 1 hour and 10 minutes or until an instant-read meat thermometer registers 140°F/60°C when inserted into the center of the pork roast. As the pork roasts in the oven, turn it occasionally to ensure it browns evenly.
Remove the pork from the oven and brush the Dijon mustard over the top and sides of the pork. Sprinkle 2/3 cup/25 g of the parsley over a work surface. Roll the mustard-coated sides of the pork in the parsley to coat, patting the parsley so that it adheres to the pork.
Allow the pork to rest for 10 minutes. Add the chicken broth to the pan drippings in the sauté pan. Stir over medium heat to loosen the pan drippings and bring the pan juices to a simmer.
Meanwhile, for the mushrooms:.
Place another large sauté pan over moderate heat. Drizzle the remaining 2 tablespoons/30 ml of olive oil over the hot pan. Add the shallots and sauté for 1 minute or until soft.
Add the garlic and continue to sauté for a further 1 minute. Add the chanterelles and sauté for about 8 minutes or until the chanterelles are tender and juices form. Stir in the remaining parsley and season with salt and pepper.
To serve: Divide the mushrooms among 4 serving plates. Cut the pork roast into thin slices and transfer the pork slices to the plates. Drizzle the pan juices over the pork. Shave the truffle into thin slices over the pork and serve.