Preheat oven to 350 degrees. Prepare 2 to 3 baking sheets by lining with parchment paper or silicone liners. Set aside.
Add flour, baking powder, baking soda, salt, and spices to a large bowl and whisk together. Add oats and stir together.
In a bowl fitted for a stand mixer, cream butter until light and fluffy. Add sugars and beat until fluffy, about 2 minutes. Add pumpkin, egg yolk, and vanilla extract and mix until combined. Add flour mixture and mix until just combined.
Using a cookie scoop, scoop a ball of cookie dough and roll into a perfect ball. Place cookie balls on baking sheet about 2 inches apart. Using 2 fingers, flatten the cookie balls into flat circles.
Bake cookies in preheated oven for 9-10 minutes or until the edges of the cookies turn golden brown. Remove from oven and cool fro 5 minutes before transferring to wire racks to finish cooling. Assemble sandwiches with filling recipe below after cookies cool completely.