Whisk pumpkin, oil, brown sugar, granulated sugar, eggs, and vanilla. Stir in flour, pumpkin pie spice, baking powder, baking soda, and salt just until combined.
Coat a 13-by-9-inch pan with baking spray. Pour in batter and smooth the surface.
Bake 40 to 45 minutes, until a pick in the center comes out clean. Cool completely in the pan.
Beat softened cream cheese until smooth. Add butter, vanilla, and pumpkin pie spice; beat until creamy. Mix in powdered sugar on low, then beat faster until fluffy, about 1 minute.
Spread frosting over the cooled bars and cut into squares. Refrigerate leftovers.
Recipe Notes
Adapted from The Pioneer Woman. Original recipe: https://www.thepioneerwoman.com/food-cooking/recipes/a44156838/pumpkin-bars-recipe/