Preheat the oven to 350°F. Line a 10x15 inch baking dish with parchment paper, this will help you lift the bars out, set aside.
In a large bowl, stir together the flour, pumpkin spice, baking powder, baking soda, and salt.
In another large bowl, whisk together the eggs, sugar, butter, pumpkin puree, and vanilla until smooth.
Add the dry ingredients and stir it together until there are no dry patches.
Pour the batter into the prepared baking dish and smooth out the top.
Bake for 30-35 minutes until a toothpick inserted into the center comes out clean. Place on a wire rack to cool completely.
While the bars cool, make the frosting by placing the cream cheese and butter in the body of a stand mixer with the paddle attachment or a large bowl with an electric hand mixer and cream until smooth.
Add the powdered sugar and mix until combined. Add the cinnamon and vanilla, stir to combine. Scrape down the sides as needed. Whip the frosting at medium speed for 2 minutes until light and fluffy.
Once the bars are cooled, add the frosting, cut, and serve.