Preheat the oven to 375 degrees F.
Spray a 3-quart baking dish with non-stick spray.
Melt the butter in a skillet and then cook the garlic until it’s fragrant
Whisk the flour into the butter and cook until it takes on a tan color (a blond roux)
Pour the half & half into the skillet and stir continuously until the sauce thickens.
Add the Parmesan cheese and whisk through.
Stir in the parsley and pepper.
Place the cooked pasta & cooked chicken in a bowl, add the Alfredo sauce and stir through.
Pour the pasta mixture into the greased casserole and top with the mozzarella.
Bake uncovered for 20-30 minutes until the top is bubbly and just starting to brown.