Preheat the oven to 375°F (190°C). Grease a 9x5-inch loaf pan or line it with parchment paper.
In a skillet, heat the olive oil over medium heat. Add the chopped onion, bell pepper, and garlic, and sauté for 5-7 minutes until softened. Remove from heat and allow to cool slightly.
In a large mixing bowl, combine the ground beef, sautéed vegetables, provolone cheese, breadcrumbs, egg, Worcestershire sauce, salt, and pepper. Mix until everything is evenly incorporated.
Transfer the mixture into the prepared loaf pan and shape it into a loaf.
In a small bowl, mix the ketchup, mustard, and brown sugar. Spread the sauce evenly over the top of the meatloaf.
Bake in the preheated oven for 55-60 minutes, or until the meatloaf reaches an internal temperature of 160°F (71°C).
Let the meatloaf rest for 10 minutes before slicing.
Garnish with fresh parsley if desired and serve with mashed potatoes, roasted vegetables, or a side salad.