Preheat your oven to 375°F (190°C). Prepare the bell peppers by slicing off the tops (about 1/2 inch) and carefully removing the seeds and membranes. If the peppers wobble, slice a thin layer off the bottom to create a stable base, being careful not to cut through.
(Optional Blanching Step) For more tender peppers, bring a large pot of salted water to a boil. Add the bell peppers and blanch for 3-5 minutes, then immediately transfer them to an ice bath to stop cooking. Drain well.
In a large skillet or Dutch oven, heat olive oil over medium-high heat. Add the ground beef and chopped onion. Cook, breaking up the meat with a spoon, until the beef is browned and the onion is softened, about 6-8 minutes. Drain any excess fat.
Add the minced garlic to the skillet and cook for another minute until fragrant. Remove from heat.
In a large bowl, combine the browned meat and onion mixture with the partially cooked rice, 1/2 can of crushed tomatoes (reserve the other half for the sauce), tomato paste, Worcestershire sauce, dried oregano, 1/4 cup chopped fresh parsley, salt, and black pepper. Mix thoroughly until well combined.
Spoon the filling evenly into each prepared bell pepper. Arrange the stuffed peppers upright in a 9x13 inch baking dish.
In a small bowl, mix the remaining 1/2 can of crushed tomatoes with the 1 can of tomato sauce and 1/2 cup of water or beef broth. Pour this sauce around the base of the peppers in the baking dish.
Cover the baking dish tightly with aluminum foil. Bake for 30 minutes. Remove the foil, and if using, sprinkle the shredded cheddar cheese over the top of each pepper.
Return the uncovered dish to the oven and continue baking for another 20-30 minutes, or until the peppers are tender and the cheese is melted and bubbly. The cooking time will vary depending on the size and initial tenderness of your peppers.
Carefully remove the baking dish from the oven. Let the stuffed peppers rest for 5-10 minutes before serving. Garnish with additional fresh parsley, if desired. Serve hot and enjoy!