Step 1: Cook the Pasta and Broccoli

1. Preheat the oven to 375°F (190°C).
2. Bring a large pot of salted water to a boil. Add the pasta and cook according to package instructions until al dente, about 8-10 minutes.
3. In the last 3 minutes of the pasta cooking time, toss in the broccoli florets. This will blanch the broccoli while the pasta finishes cooking, saving time and pans.
4. Drain both the pasta and broccoli together, and set them aside.

Step 2: Prepare the Chicken and Alfredo Mixture

1. If using leftover or rotisserie chicken, shred or cube it into bite-sized pieces.
2. In a large mixing bowl, combine the cooked pasta, broccoli, chicken, Alfredo sauce, Parmesan cheese, garlic powder, and ½ cup of the shredded mozzarella. Stir until everything is well coated. Season with salt and pepper to taste.

Step 3: Assemble the Casserole

1. Grease a 9×13-inch casserole dish with cooking spray or a little butter.
2. Pour the Alfredo, chicken, and broccoli mixture into the prepared dish, spreading it evenly.
3. Sprinkle the remaining ½ cup of shredded mozzarella cheese over the top of the casserole.

Step 4: Prepare the Panko Breadcrumb Topping

1. In a small bowl, mix the Panko breadcrumbs with the olive oil or melted butter until the breadcrumbs are evenly coated. This will give them a nice golden color and extra crunch during baking.
2. Sprinkle the Panko mixture evenly over the top of the casserole, creating a crispy topping.

Step 5: Bake the Casserole

1. Place the casserole in the preheated oven and bake for 20-25 minutes, or until the top is golden brown and the cheese is bubbly.
2. If the breadcrumbs aren’t browning to your liking, you can turn on the broiler for the last 2-3 minutes of baking, but watch carefully to prevent burning.

Step 6: Garnish and Serve

1. Once baked, remove the casserole from the oven and let it rest for 5 minutes before serving.
2. Garnish with freshly chopped parsley, if desired, for a pop of color and freshness.