Preheat your oven to 180C/375F. Lightly coat a 9×13-inch baking dish with nonstick spray. Place the bell pepper halves in the dish.
Add the oil to a large non-stick pan and place it over medium heat. Add the beef and onion. With a wooden spoon or spatula, break the meat into small pieces. Cook for 6-7 minutes, or until the beef is browned.
Add the taco seasoning then pour in the can of diced tomatoes along with the juices, and let it simmer. Remove off the heat.
Stir through the cooked rice and half the cheese.
Evenly distribute the mixture amongst the eight bell pepper halves and top with the remaining cheese.
Bake the stuffed peppers for 20-25 minutes, or until the cheese has melted.
TO STORE: You can store leftovers in the refrigerator in airtight containers for up to 4 days.TO FREEZE: Place the cooked and cooled peppers in a shallow container and store them in the freezer for up to 6 months. TO REHEAT: Thaw and then heat in the microwave to enjoy them again.