Preheat the oven to 400 degrees. Grease a 9x13” baking dish with cooking spray, or line a large baking sheet with foil.
Rub the bell peppers with 1 tablespoon of the olive oil and season the inside with salt and pepper, to taste. Place the peppers in the prepared baking dish and roast for 20-30 minutes until softened but slightly undercooked.
While the peppers roast, prepare the filling. Heat the remaining 2 tablespoons of olive oil in a large sauté pan over medium heat. Add the ground beef, salt and pepper and cook for about 3 minutes, breaking into chunks with a wooden spoon. Add the onion and cook for 5 minutes or until softened. Drain any excess grease as needed.
Add the garlic and oregano and cook for 30 seconds, then add the tomato sauce and tomato paste and simmer for about 5- 10 minutes on medium low heat.
Remove the pan from heat and adjust the seasoning as necessary, then stir in the rice and 1 cup of grated mozzarella cheese.
Stuff the peppers with the filling, and top with the remaining ½ cup mozzarella cheese. Bake for about 10-15 minutes or until the cheese has melted and the peppers have reached the desired doneness.
Remove from heat, sprinkle the fresh basil over the top and enjoy!