Preheat the oven to 375°F. Coat a baking dish (9 inches x 11 inches) with oil/butter.
Cook pasta until al dente in a large pot with boiling water seasoned with salt.
Season chicken breast with salt and pepper and cook in some olive oil till done (Cut chicken breast into strips for faster cooking). Do not overcook. Chop and keep aside.
Sweat the mushrooms in 1/2 tbsp butter and keep aside. Heat the remaining butter in a large pan over low-med heat.
Add the garlic and cook for 30 seconds. Then add flour and cook for 1 minute. Pour in the milk and cream, then simmer, stirring constantly, until sauce has just thickened.
Add the Parmesan cheese and 1/2 cup shredded mozzarella to the milk mixture, along with salt and pepper to taste.
Stir until cheese has melted. (The Alfredo sauce is ready at this point.)
Mix in the pasta, chicken, mushrooms and olives and coat everything with the sauce properly. Pour the pasta mixture into the prepared pan, and top with remaining mozzarella cheese.
Bake for 15 - 20 minutes or until pasta is bubbly and cheese has just started to brown.
Sprinkle dried mixed herbs or parsley over the top, then serve hot.