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 boil. Cook ravioli according to package directions for 3–5 minutes until al dente. Drain thoroughly in a colander.
03 - In a large mixing bowl, combine cooked ravioli, chicken, Alfredo sauce, milk, Italian seasoning, and black pepper. Gently fold together until evenly coated.
04 - Transfer mixture to the prepared baking dish. Spread mozzarella and Parmesan cheese evenly across the top.
05 - Cover dish tightly with aluminum foil. Bake for 20 minutes to heat through.
06 - Remove foil and bake an additional 10–15 minutes until cheese is golden brown and bubbly.
07 - Let casserole rest for 5 minutes before serving. Garnish with chopped fresh parsley if desired.