Preheat the oven to 350°F.
In a large mixing bowl, combine ground beef, onion, bell pepper, mushrooms, garlic powder, salt, and black pepper. Mix until well combined.
Add the breadcrumbs, eggs, ketchup, Worcestershire sauce, and Dijon mustard to the meat mixture. Mix until all ingredients are evenly incorporated.
Transfer the meat mixture to a loaf pan and shape it into a loaf. Pour the beef broth over the top of the meatloaf.
Bake in the preheated oven for 1 hour. After 45 minutes, sprinkle the shredded provolone cheese on top of the meatloaf and return to the oven for the remaining 15 minutes.
Once cooked, let the meatloaf rest for 10 minutes before slicing. Serve warm.