Preheat oven to 350 degrees. With cooking spray, spray a 9 x 13-inch baking pan and arrange halved peppers, rounded sides down, in a single layer. Set aside.
In a large skillet, heat olive oil over medium heat, add onion and sauté 2 to 3 minutes or until translucent. Add garlic and stir for 30 seconds. Add prepared crumbled stuffing and mix well. Add salt and pepper to taste.
Divide stuffing mixture between pepper halves, pressing down firmly and rounding the tops. Bake in the preheated oven until peppers are tender, about 35 minutes.
Sprinkle 1 tablespoon cheese on each and return to oven until cheese melts and is lightly browned, 5 to 10 minutes longer. Garnish with minced parsley and serve hot.