Preheat oven to 450. In a small sauce pan melt the butter over medium heat. Whisk in flour, then whisk in milk a little at a time to prevent clumping. Whisk in garlic powder and salt and continue stirring until thickened, about 4 or 5 minutes. Remove one Mama Mary's pizza crust from the package and spread the white sauce evenly on top. Thinly slice the tomato and roughly chop the spinach, then arrange evenly over the sauce. Top with mozzarella, followed by parmesan. Bake for 9-10 minutes, until edges are lightly brown and cheese is melted and bubbly. Cool for 2-3 minutes before slicing.