Preheat oven to 400 degrees. Wash and dry the outside of the bell peppers.
Start cooking your rice according to the package directions and set aside once done while prepping the rest of the dish.
Carefully cut the tops off each of the bell peppers. Discard the green stem, but keep the top pepper flesh around the green stem. Dice the pepper tops.
Remove the seeds and the membranes from the peppers. Place the empty bell peppers in a 9x9 baking dish. If the bottoms of the peppers do not sit flat, carefully slice a thin amount off the bottoms.
In a large skillet, over medium to medium high heat, add the olive oil, diced yellow onion and diced pepper tops. Using a wooden spoon stir often, and cook uncovered for 5-7 minutes, until softened and opaque.
Add the 1 lb of lean ground beef and the tablespoon of minced garlic. Continue using the wooden spoon to stir often and break up the ground beef as it cooks. Cook uncovered until ground beef is cooked completely.
Remove the ground beef mixture from the heat and drain. Return the ground beef mixture to the skillet and the stovetop.
Reduce the heat to medium, add the can of petite diced tomatoes and the cup of cooked rice. Stir.
Add the kosher salt, black pepper, oregano and red pepper flakes. Stir to combine. Reduce the heat to low.
Allow the ground beef mixture to cook for another 5 minutes. Remove from the heat.
Evenly fill the peppers with the ground beef mixture. Sprinkle 2 teaspoons of the grated parmesan cheese over the top of the ground beef mixture.
Sprinkle 1 ½ tablespoons of the mozzarella cheese on top of the peppers. (we want enough cheese to lightly cover the filling but we still want the filling to slightly pop through the gooey cheese)
Pour ½ cup of water into the bottom of the pan to help steam the stuffed peppers. Spray the foil with cooking spray and cover with foil and bake at 400 degrees for 35 minutes. The cooking spray will help preventing the cheese to stick to the foil as it bakes.
Remove the foil and bake for an additional 10 minutes. Serve while hot.
Leftover peppers should be stored in a shallow, airtight container in the fridge. When properly stored, they will last for 3 to 5 days.To Freeze: Stuffed peppers are the perfect food to freeze! Just place them in an airtight container in the freezer or wrap them individually in plastic wrap and store them in a freezer bag for up to 3 months. When ready to eat, bake them at 350 degrees for about 20-30 or until heated to your preference.