01 - Heat a large nonstick skillet over medium-high heat. Add ground beef and cook, breaking it up with a wooden spoon, until evenly browned, about 5–7 minutes. Drain excess fat if necessary.
02 - Add diced onion, bell pepper, mushrooms (if using), and garlic to the pan. Sauté until softened and fragrant, about 5 minutes.
03 - Stir in Worcestershire sauce, ketchup, Dijon mustard, smoked paprika, salt, pepper, and chili flakes. Mix well to coat the beef and vegetables evenly.
04 - Pour in beef broth, bring to a gentle simmer, and cook for 5–7 minutes until the mixture thickens slightly and the flavors meld together.
05 - Reduce the heat to low. Sprinkle shredded provolone cheese evenly over the beef mixture. Cover the pan and let the cheese melt, about 2 minutes.
06 - Stir the cheesy mixture together until well-combined and creamy throughout.
07 - Spoon generous portions of the filling onto toasted buns. Garnish with chopped parsley or sliced jalapeños, if desired. Serve immediately while hot.