Preheat your oven to 400°F (200°C).

In a large skillet, heat olive oil over medium heat. Add chopped onion and sauté for about 7 minutes until soft and translucent.

Stir in minced garlic and tomato paste, cooking for an additional minute until fragrant.

Add ground beef to the skillet, breaking it up with a spatula. Cook for about 6 minutes, stirring regularly until no longer pink.

Stir in cooked brown rice, canned diced tomatoes, oregano, salt, and black pepper. Let the mixture simmer for another 5 minutes.

Prepare bell peppers by cutting off the tops and removing the seeds. Drizzle the insides lightly with olive oil and season with a pinch of salt.

Carefully fill each bell pepper with the beef and rice mixture, packing it in gently. Arrange stuffed peppers upright in a baking dish.

Cover tightly with aluminum foil and bake for about 35 minutes.

After 35 minutes, remove the foil and sprinkle tops with shredded Monterey Jack cheese. Bake uncovered for another 10 minutes.

Remove from oven and let cool slightly. Sprinkle chopped parsley over the tops before serving.