Preheat oven to 350°F.
Cut off the top 1/2 inch of each bell pepper and keep the tops. Remove seeds and membrane from peppers. Remove stems from tops if desired. Wash well.
Place prepared peppers in a large saucepan or stock pot with enough water to cover and a pinch of salt. Bring to a boil and cook 5 minutes. Drain and set peppers aside.
In a large skillet, brown ground beef over medium-high heat and drain off fat. Add mushrooms, zucchini, onion, garlic, salt and basil to the ground beef. Cook until vegetables are tender, stirring often. Remove from heat and cool slightly. Stir in rice and 1 1/2 cups of the Cooper Cheese.
Place peppers in a shallow baking dish. Lightly stuff each pepper with filling. Spoon tomato sauce over the peppers. Cover and bake 30 minutes.
Remove from oven and uncover. Add remaining 1/2 cup of Cooper Cheese to each of the peppers and bake another 5 minutes, or until cheese is melted.
Garnish with fresh basil leaves.