In conventional oven, par-bake crust for 5-8 minutes.
Toss chicken with garlic powder in bowl.
Spread Alfredo sauce over crust. Top with 1/2 cup Shredded Monterey Jack and Mild Cheddar cheese. Top evenly with chicken, onion, mushrooms, spinach and remaining cheese.
Bake pizza 10-15 minutes or until cheese is melted and crust is browned and crispy; slice to serve.