Whisk dry ingredients: In a large bowl, combine the flour, pumpkin pie spice, cinnamon, baking soda, and salt.
Cream butter and sugars: Using a mixer, beat the butter, brown sugar, and granulated sugar until creamy. Blend in the egg yolk and vanilla, then the pumpkin puree.
Combine with dry mix: Gradually add the dry ingredients to the wet mix, then fold in the oats.
Chill dough: Cover the dough with plastic wrap and refrigerate for 30 minutes to firm up.
Prep for baking: Preheat the oven to 350°F and line baking sheets with parchment paper.
Shape cookies: Scoop dough onto sheets, roll into balls, and slightly flatten.
Bake: Bake each batch for 9-12 minutes until lightly browned. Cool on the sheet before transferring to a rack.