Mount the oven to 350 degrees.
Whisk together the pumpkin, eggs, sugar, and oil in a medium basin until light and airy.
Combine the flour, baking powder, cinnamon, salt, and baking soda in a separate basin. Beat the dry ingredients into the liquid ingredients until a smooth batter forms.
Bake for 30 minutes in a greased 15-by-10-inch baking pan containing the batter.
Prepare the frosting while the bars bake by beating together cream cheese, butter, vanilla, powdered sugar, and cinnamon in a medium basin.
Completely chill the bars prior to frosting. You may cut the bars in advance, then frost or pour on frosting before cutting.