Preheat your oven to 375°F (190°C).

Cut the tops off the bell peppers and remove the seeds and membranes. Place them upright in a baking dish.

In a large skillet, heat the olive oil over medium heat. Add the sliced onion and mushrooms, sautéing for about 5-7 minutes until softened. Stir in the minced garlic for the last minute.

Add the thinly sliced beef to the skillet with the sautéed vegetables. Season with salt, pepper, Worcestershire sauce, and Italian seasoning. Cook until the beef is browned and cooked through, about 5-6 minutes.

Spoon the beef and vegetable mixture into each bell pepper, packing it tightly. Top each pepper with shredded provolone cheese.

Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 10-15 minutes until the cheese is melted and bubbly.

Garnish with chopped fresh parsley before serving.