Preheat the oven to 375°F (190°C).
Cut the tops off the bell peppers and remove the seeds and membranes. Place the peppers upright in a baking dish.
In a skillet, heat the olive oil over medium heat. Add the diced onion and cook until softened, about 4-5 minutes. Stir in the minced garlic and cook for another minute until fragrant.
Add the ground beef to the skillet and cook until browned, breaking it apart with a spoon. Drain any excess fat.
Stir in the salt, black pepper, Worcestershire sauce, and mix well. Remove from heat.
Fill each bell pepper with the beef and onion mixture, packing it in tightly.
Sprinkle the shredded provolone cheese generously on top of each stuffed pepper.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 5-10 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let cool for a few minutes before serving. Garnish with chopped parsley if desired.