Preheat the oven to 350°F. Generously spray a 9x13 baking dish with nonstick spray. Set it aside.
In a medium-sized mixing bowl, whisk together flour, pumpkin pie spice, baking powder, baking soda, ground cinnamon, ground ginger and salt. Set it aside.
Using either a stand mixer, or a medium sized mixing bowl and a handheld mixer on medium speed, beat together the vegetable oil, granulated sugar, canned pumpkin puree and vanilla extract until the ingredients are combined. Scrape down the sides of the bowl with a silicone spatula.
With the mixer speed on low, add the eggs 1 at a time, mixing well after each egg.
Keeping the mixer speed on low, slowly add the dry ingredients to the pumpkin mixture. Blend just until all the ingredients are well combined.
Evenly pour the batter into the prepared pan. Bake for 22 - 25 minutes, until a toothpick inserted comes out clean. Allow the pumpkin bars to cool completely.
Using a medium sized mixing bowl and a handheld mixer on medium-high speed, cream together the cream cheese, butter and clear vanilla flavoring for about 1 - 1 ½ minutes.
Lower the mixer speed to low, slowly alternate the powdered sugar and milk. Increase the mixer speed to medium and mix until the frosting is smooth.
Using a silicone spatula, evenly spread the cream cheese frosting over the cooled pumpkin bars, and slice either 5 slices x 5 slices or 5 slices x 6 slices.