Preheat oven to 350 degrees F. In a medium bowl, whisk flour, baking powder, cinnamon, salt and baking soda.
In a large bowl, beat eggs, sugar, oil and pumpkin until light and fluffy.
Gradually add the dry ingredients, mixing well after each addition.
Spread batter in a greased 15x10x1 baking pan. Bake at 350 degrees F for 25-30 minutes or until a toothpick inserted comes out clean. Remove from oven to a wire rack and cool completely.
Frosting
Cream together butter and cream cheese until smooth and fluffy
Gradually add the powdered sugar, beating until mixture is smooth
Add vanilla and spice, if using, beat until smooth. Gently frost bars. Cut and serve!