Preheat oven to 350 and grease a 10x15 inch baking pan. (I use butter wrappers to grease pan).
Whisk the flour, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice together in a large bowl. Set aside.
Whisk the oil, eggs, brown sugar, granulated sugar, maple syrup, pumpkin, and vanilla extract together until combined.
Pour the wet ingredients into the dry ingredients and use a mixer or a whisk until completely combined. Batter will be thick.
Spread batter into the prepared pan. Bake for 28 to 35 minutes or until toothpick inserted in the center comes out clean.
Remove the bars from the oven and set the pan on a wire rack. Cool bars completely.
Make the frosting: In a large bowl using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the cream cheese and butter together on high speed until smooth and creamy. Add confectioners' sugar, vanilla, pumpkin pie space, and salt. Beat on low speed for 30 seconds, then switch to high speed and beat for two minutes. If you want the frosting a little thicker, add an extra 1/4 cup of confectioners' sugar. Spread the frosting on the cooled bars. This will help set the frosting. Refrigerate for 30 minutes before slicing and serving. This makes cutting easier and less messy.