Preheat your oven to 350°F (175°C).
Wash and chop the vegetables. Finely chop the green bell pepper, onion, and mushrooms. Mince the garlic. In a large skillet, heat the olive oil over medium heat. Add the chopped vegetables and garlic. Sauté for 5-7 minutes until soft.
Remove the sautéed vegetables from heat and let cool slightly. In a large mixing bowl, combine ground beef, sautéed vegetables, salt, black pepper, Worcestershire sauce, breadcrumbs, and egg. Mix until just combined.
Transfer the mixture into a loaf pan and mold it into a loaf shape. If using a baking sheet, shape it freehand about 2 inches thick.
Pour beef broth over the top of the meatloaf. Bake for 45-50 minutes until the internal temperature reaches 160°F (70°C).
During the last 10 minutes of baking, sprinkle shredded provolone cheese over the top. Return to the oven until melted and bubbly. Let rest for 10 minutes before slicing.