Preheat the oven to 375°F (190°C).

Slice off the tops of the bell peppers and scoop out the seeds and membranes.

In a large skillet, warm olive oil over medium heat and sauté diced onion for 5-7 minutes until translucent.

Add minced garlic and cook for an additional minute. Then, add the ground beef or turkey and cook until browned, about 8-10 minutes.

Mix in diced tomatoes, tomato sauce, cooked brown rice, and parsley, stirring until well combined.

Sprinkle in oregano, basil, salt, black pepper, and red pepper flakes. Stir well to incorporate.

Fill each bell pepper with the savory mixture, mounding slightly at the top.

Pour half an inch of water into the baking dish and cover with aluminum foil.

Bake covered for 30 minutes, then remove the foil.

Sprinkle cheese on top of each pepper and bake uncovered for an additional 30-40 minutes until cheese is golden brown.

Allow to cool slightly before serving.