Preheat oven to 425°.
Unroll dough onto a baking sheet coated with cooking spray; cut into 4 quarters. Pat each quarter into a 6 x 5-inch rectangle. Sprinkle garlic evenly over rectangles. Top each rectangle with 1 cup spinach, 2 onion slices, 1/3 cup mushrooms, and 3 tablespoons cheese. Bring 2 opposite corners to center, pinching points to seal. Bring remaining 2 corners to center, pinching all points together to seal. Bake at 425° for 12 minutes or until golden.