Preheat your oven to 400°F (200°C). Cook the rice according to the package directions in a small saucepan.

While the rice is cooking, heat the olive oil in a large skillet over medium heat. Add the chopped onion and sauté until it becomes soft and translucent, which takes about 7 minutes. Stir in the minced garlic and tomato paste, cooking until they release their aroma, about 1 minute. Add the ground beef to the skillet and cook it, breaking it apart with a wooden spoon, until it is browned and no longer pink, roughly 6 minutes. Drain off any excess fat from the skillet.

Mix the cooked rice and diced tomatoes into the beef mixture. Season generously with dried oregano, kosher salt, and freshly ground black pepper. Allow the mixture to simmer and thicken slightly, stirring occasionally, for about 5 minutes.

Prepare a 13"x9" baking dish by arranging the bell peppers cut side up. Drizzle them with a bit of olive oil. Fill each pepper with the beef and rice mixture, packing it in tightly. Sprinkle the shredded Monterey Jack cheese over the tops. Cover the baking dish with aluminum foil.

Bake the stuffed peppers in the preheated oven for about 35 minutes, until the peppers are tender. Then, remove the foil and continue baking for an additional 10 minutes, or until the cheese is melted and bubbly.

Before serving, garnish the peppers with chopped fresh parsley for a burst of color and flavor. Serve hot and enjoy your delicious, hearty stuffed peppers.