Preheat the oven to 375°F (190°C) and grease a loaf pan. In a large mixing bowl, combine ground beef, French onion soup mix, breadcrumbs, eggs, milk, Parmesan cheese, and Worcestershire sauce. Mix until just combined; avoid overmixing. Transfer the mixture to the prepared loaf pan, shaping it into a loaf.
In a small bowl, mix together ketchup, brown sugar, and Dijon mustard. Spread the glaze evenly over the meatloaf.
Place the meatloaf in the oven and bake for 45 minutes. Remove from the oven, sprinkle shredded cheese over the top, and return to the oven. Bake for an additional 10-15 minutes, or until the cheese is melted and the meatloaf reaches an internal temperature of 160°F (71°C).
Allow the meatloaf to rest for 10 minutes before slicing. Garnish with sautéed onions, if desired, and serve hot.