Preheat oven to 375°F (190°C). Slice the loaf of French bread in half lengthwise and scoop out some of the surface, leaving a 1-inch border intact. Spread mayonnaise evenly over both halves of the bread and place on a baking sheet. Warm the olive oil in a large nonstick skillet over medium-high heat. Add the diced onion, bell pepper, and mushrooms. Sauté until tender, about 2 minutes. Add the ground beef and cook, breaking it up into small crumbles, until browned and no pink remains, about 3 minutes. Drain off any excess fat. Stir in Worcestershire sauce, salt, and pepper. In a small bowl, whisk together cornstarch and beef broth, then add this mixture to the beef. Simmer for 2-3 minutes, stirring occasionally, until the mixture thickens slightly. Divide the beef mixture and spread it evenly between the two halves of bread. Sprinkle shredded Provolone or Monterey Jack cheese on top of the beef. Bake for 15 minutes or until the cheese is melted and starting to brown. Alternatively, you can broil it for a minute or two for extra browning. Once baked, cut into 2-inch portions for appetizers or larger portions for lunch or dinner. Garnish with red pepper flakes for added heat and color, if desired. Serve and enjoy!