01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or butter.
02 - Bring a large pot of salted water to a rolling boil. Add ravioli and cook according to package directions, typically 3–5 minutes. Drain thoroughly in a colander.
03 - In a large mixing bowl, combine cooked ravioli, shredded chicken, Alfredo sauce, milk, Italian seasoning, and black pepper. Gently fold together until all components are evenly coated.
04 - Transfer the mixture to the prepared baking dish, spreading evenly. Sprinkle shredded mozzarella and grated Parmesan cheese over the top in a uniform layer.
05 - Cover baking dish tightly with aluminum foil. Bake for 20 minutes to allow flavors to meld and sauce to heat through.
06 - Remove foil and return to oven for an additional 10–15 minutes, or until cheese is melted and golden brown with bubbling edges.
07 - Let casserole rest for 5 minutes before serving to allow sauce to thicken slightly. Garnish with fresh chopped parsley if desired.