Place oven rack in the lowest position; preheat to 450°F. Coat a large baking sheet with cooking spray.
Roll out dough on a lightly floured surface to the size of the baking sheet. Transfer to the baking sheet. Bake until puffed and lightly crisped on the bottom, 8 to 10 minutes.
Whisk pumpkin puree, tomato sauce and garlic powder in a small bowl until combined.
Spread sauce evenly over the baked crust. Top with mozzarella, Parmesan and pepperoni. Bake until the crust is crispy on the edges and the cheeses have melted, about 12 minutes.