Preheat the oven to 350°F (175°C). Grease and lightly flour a 10x15-inch baking pan, or line it with parchment paper.

In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, ginger, and salt.

In a large bowl, whisk the granulated sugar, brown sugar, oil, and eggs until smooth and well combined.

Stir in the pumpkin puree and vanilla extract until fully incorporated.

Add the dry ingredients to the wet ingredients and mix just until no streaks of flour remain. Do not overmix.

Spread the batter evenly into the prepared pan.

Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.

Remove from the oven and let the bars cool completely in the pan.

To make the frosting, beat the cream cheese and butter together until smooth and fluffy.

Add the powdered sugar, vanilla extract, and salt, then beat until creamy and spreadable.

Spread the frosting evenly over the cooled pumpkin bars.

Cut into squares and serve.