In a large bowl whisk together the flour, pumpkin spice, baking soda and salt.
In a separate large bowl, beat together the butter, brown sugar and white sugar until fluffy.
Mix in the egg yolk and vanilla extract.
Blot the pumpkin puree with a paper towel and squeeze out the excess liquid. Then beat the pumpkin into the butter mixture.
With the mixer on low speed, mix the dry ingredients into the pumpkin batter.
Mix in the oats.
Cover the bowl with plastic wrap and chill in the fridge for 30 minutes.
When ready to bake, preheat the oven to 350F degrees and line cookie sheets with parchment paper or silicone baking mats.
Using a 1.5 tablespoon cookie scoop (or a spoon and your hands), scoop the dough, roll it into balls, and place 2 inches apart on the lined cookie sheets. Flatten each cookie down so that it's about 1/3 inch thick.
Bake the cookies 1 sheet at a time on the middle rack of the preheated oven for about 8-10 minutes, or until the tops look just set.
Cool on the cookie tray for at least 10 minutes before transferring to a wire rack.