Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper.
In a large bowl, sift together the flour, baking powder, baking soda, cinnamon, and salt.
In another bowl, whisk together the brown sugar and oil until blended, then add pumpkin puree, eggs, and vanilla.
Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
Drop rounded tablespoons of the batter onto the prepared baking sheets, leaving some space between each.
Bake for about 12-15 minutes, or until the pies spring back when touched lightly.
Allow to cool on the sheets for a few minutes before transferring to wire racks to cool completely.
Prepare your favorite filling (such as cream cheese frosting) and spread between two Pumpkin Whoopie Pie cookies to sandwich them together.