Preheat the oven to 350°F. Cook the pasta according to the packet directions. Drain. Do not rinse and set aside.
While the pasta is cooking, combine the marinara sauce, shredded cooked chicken, Italian seasoning, onion powder, garlic powder and red pepper flakes in a large mixing bowl. Season to taste with salt and pepper.
Once the pasta has been cooked and drained, add to the marinara sauce mixture. Stir gently until well combined.
Transfer the pasta mixture to a 9 x 13 inch baking dish. Top with the shredded mozzarella and parmesan cheeses. Bake for 30 minutes, or until the cheese is bubbly and golden.
Garnish the casserole with the chopped fresh parsley, if using, before serving.