In a saucepan over medium high heat, add butter. Once melted add garlic and saute for 3 minutes. Then whisk in flour and cook for 2 minutes. Next whisk in heavy cream and cook for 2 minutes. Then add pepper and broth and cook for 2 minutes. Last add parmesan cheese and cook until fully incorporated.
Add chicken and seasoning to a bowl and toss to coat.
Spray each of the baking dishes lightly with cooking spray. Layer each dish with half of the potatoes, half of the spinach then half of the chicken. Sprinkle each with a cup of mozzarella cheese. Next ladle in half of the alfredo, evenly, into each pan. And last layer on half of the remaining parmesan cheese on each.
Place in oven and bake for 1 hour. Let cool at least 5 minutes before serving.