Preheat oven to 350℉.Line a baking pan with parchment paper and lightly spray with non-stick cooking spray. In a small bowl, sift together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.
Using a stand or hand mixer, blend the sugar and oil until well combined. Add the pumpkin purée and then the eggs, one at a time, mixing until the batter is light and fluffy.
Gradually add the dry ingredients to the pumpkin mixture, mixing at low speed until just combined and the batter is smooth.
Pour the batter into your prepared pan and bake for 30 minutes. Remove from the oven and let cool for 20 minutes, then cover with plastic wrap or Press-n-Seal to lock in moisture as the bars finish cooling. Allow them to cool completely before frosting.