Step 1: Prepare the Bell Peppers
Preheat the 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.
Step 2: Cook the Filling
Heat olive oil in a large skillet over medium heat. Add the diced onion and sauté for 3–4 minutes until softened.
Add the garlic and cook for 1 minute, stirring to avoid burning.
Add the ground beef and cook until browned, about 5–6 minutes. Drain any excess grease from the pan.
Stir in the cooked brown rice, diced tomatoes, oregano, cumin, salt, and black pepper. Simmer for 5 minutes to allow the flavors to meld.
Step 3: Assemble the Peppers
Spoon the beef and rice mixture into the prepared bell peppers, filling them generously.
Cover the baking dish with foil and bake for 30 minutes.
Step 4: Add Cheese and Finish Baking
Remove the foil, sprinkle the tops of the peppers with shredded cheese, and bake uncovered for an additional 10 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let the peppers cool slightly. Garnish with chopped parsley before serving.