Step 1: Prepare the Peppers
1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Cut and Clean: Slice the tops off the bell peppers and remove the seeds and membranes. Place the peppers upright in a baking dish.

Step 2: Make the Filling
1. Combine Ingredients: In a large mixing bowl, combine the cooked chicken, Alfredo sauce, cooked rice or quinoa, half of the mozzarella cheese, garlic powder, Italian seasoning, salt, and pepper. Mix until well combined.

Step 3: Stuff the Peppers
1. Fill Peppers: Spoon the chicken Alfredo mixture into each bell pepper, packing it down gently. Top each stuffed pepper with the remaining mozzarella cheese and sprinkle with Parmesan cheese.

Step 4: Bake
1. Cover and Bake: Cover the baking dish with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.

Step 5: Serve
1. Garnish: Remove from the oven and let cool slightly. Garnish with fresh parsley if desired. Serve warm.