01 - Preheat your 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 the ravioli and cook according to package directions, typically 3–5 minutes. Drain thoroughly in a colander.
03 - In a large mixing bowl, add the cooked ravioli, shredded chicken, Alfredo sauce, whole 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 it into an even layer. Distribute the mozzarella and Parmesan cheese uniformly across the top.
05 - Cover the dish tightly with aluminum foil. Bake for 20 minutes to allow flavors to meld and the filling to heat through completely.
06 - Remove the foil and return to the oven for an additional 10–15 minutes, or until the cheese is melted, golden brown, and bubbly around the edges.
07 - Let the casserole rest for 5 minutes before serving to allow the sauce to thicken slightly. Garnish with fresh chopped parsley if desired.