In a mixing bowl, whisk together the flour, cinnamon, allspice, cloves, baking soda, and salt. Set aside.
In the bowl of a stand mixer, cream together the butter with both sugars until well combined, about 2 minutes. Add in the egg yolk and vanilla extract and mix until well combined. Stir in the pumpkin puree.
Slowly add the flour mixture and mix until just combined. Scrape the sides of the bowl down and add the oats. Mix once more until just combined.
Refrigerate the dough for 30 minutes.
Preheat your oven to 350 degrees. Line two baking sheets with parchment or baking mats.
Use a tablespoon cookie scoop to drop dough onto the baking sheets, making sure to leave some space in between each cookie.
Bake for 9-11 minutes, until the edges of the cookies are slightly browned. Remove from the oven and allow to cool slightly.
While the cookies are cooling, make the glaze. Mix together the powdered sugar and a couple of teaspoons of water until completely smooth. Add a couple more teaspoons of water if needed. The glaze should easily drizzle, but not be too thin.
Using a spoon, drizzle the glaze over the cookies.