Let pizza dough come to room temperature and heat oven to 450 degrees. If you have a pizza stone, place it in the oven.
To make garlic butter, melt butter over medium heat in a small pan over medium heat. Add garlic and onion and cook until softened, about 2 minutes. Add Italian seasoning, red pepper flakes, and salt and remove from heat.
To make sauce, melt butter in a medium pan. Whisk in flour and cook for 1 minute. Gradually whisk in milk. Let cook for about 2 minutes. Mixture will be very thick. Stir in salt, pepper, and cheese. Remove from heat.
Divide pizza dough in 2 pieces and roll or stretch into approximately a 10-inch round. Place on a lightly floured pizza peel or baking sheet with no edges.
Spread half of garlic butter on dough and cover with approximately 1/2 cup of the sauce. You can use more if you want it heavy on sauce.
Sprinkle chicken with thyme and poultry seasoning. Scatter 1/2 of chicken on dough.
Top with spinach leaves, half of mozzarella, bacon, and green onion.
Slide pizza off of pizza peel onto a the pizza stone or onto a baking sheet if you are not using a pizza stone.
Bake for 8 to 12 minutes of until crust is golden brown.