Make It Now:

1. Cook the pasta and broccoli: Bring a large pot of water to a boil and add a generous pinch of salt (skip the salt if using jarred Alfredo sauce). Cook the pasta until al dente according to package instructions. Add the broccoli to the boiling water during the last 2 minutes of cooking, just until crisp tender. Drain the pasta and broccoli together and set aside. 
2. Preheat the oven: Preheat your oven to 375°F (190°C). Lightly grease a 9×9-inch baking dish.
3. Prepare the Alfredo Sauce: (skip this step if using a jar from the store) Set the same pot you made the pasta in over medium heat and melt the butter until it begins to bubble gently. Using a whisk, stir in the flour and whisk for about 1 minute. Whisk in the chicken broth and the milk until smooth. Turn up heat and bring to a low simmer. Cook for 1-2 minutes, whisking continually, until slightly thickened. Remove from the heat. Whisk in 1 cup grated Parmesan, salt, and pepper until well combined.
4. Combine: Stir garlic powder and Italian seasoning into the sauce. Then, add the cooked pasta and broccoli, rotisserie chicken, and 1/2 cup shredded mozzarella (reserve the rest) and gently stir until evenly combined.
5. Assemble the casserole: Pour the mixture into the prepared 9×9-inch pan. Sprinkle 1/4 cup Parmesan cheese and the remaining 1/2 cup mozzarella cheese evenly over the top.
6. Bake: Bake on the middle rack for 20-25 minutes, or until the cheese is melted and bubbly. Optional: Turn on the broiler for 1 to 2 minutes, just until it starts to get a little golden on top (watch closely!). Top with fresh chopped parsley, if desired. Serve warm.

Freeze For Later: Assemble the casserole (through Step 5), but do not bake. Cover tightly with several layers of plastic wrap and/or foil or an air-tight lid, label, and freeze.

Prepare From Frozen: Thaw about 24-48 hours in the refrigerator. Bake according to directions in Step 6. It may bake a little longer if it’s still cold from the fridge.