Preheat oven to 350 degrees F.
In a large bowl, combine pumpkin, sugar, eggs and oil with an electric mixer until well combined.
Add flour, baking soda, baking powder, pumpkin pie spice, cinnamon and salt to the wet ingredients and mix by hand until just combined.
Pour batter into a 9x13" baking pan that has been sprayed with non-stick cooking spray.
Bake for approximately 30-40 minutes. Bars should be starting to set up, but remember this is more like a brownie than a cake, it should seem a bit undercooked in the center, but not still be wet.
Remove from oven and allow to cool completely on a wire cooling rack.