In a medium mixing bowl, whisk together the gluten free flour blend, pumpkin pie spice, cinnamon, baking powder, baking soda, and salt until combined.
In a large mixing bowl, stir together the sugar, pumpkin puree, melted butter and vanilla until completely combined.
Stir the dry ingredients into the wet ingredients until combined.
Add the oats to the mixture and stir until completely combined.
Chill the dough in the refrigerator for at least 20 minutes.
Preheat oven to 350° F. Line 2 baking pans with Silpat liners or parchment paper.
Using a 1.5-tablespoon cookie scoop, drop the dough onto the lined baking pans 2 inches apart.
After dropping the dough onto the pans, roll each scoop of dough between the palms of your hands to form balls. Then use your fingers to gently press the dough balls flat. (Note: The dough will not spread.)
Bake for 12-14 minutes, or until the cookies are set and the bottoms are lightly browned.
Cool the cookies for 5 minutes on the pan, then transfer to a wire rack to cool completely.
Be sure to use pumpkin puree, not pumpkin pie filling. Pumpkin pie filling has added sugar in it and will make the cookies overly sweet.
Stirring the dry ingredients into the wet ingredients prevents overmixing the dough. Over mixing the dough can make the cookies tough.
Chilling the dough will solidify the melted butter and keep the cookies from spreading. It will also make it easier to roll the dough into balls.