Drain canned pumpkin by spreading it on a paper towel–lined cutting board. Pat with additional paper towels and let stand for 15 minutes. Replace with fresh paper towels if needed. You should have about 135–140 g (½ cup) well-drained puree.
Preheat oven to 350°F (175°C). Line baking sheets with parchment paper and set aside.
In a medium bowl, whisk flour, oats, baking soda, baking powder, salt, cinnamon, nutmeg, and ginger.
In a large bowl, beat butter, brown sugar, and granulated sugar until light and fluffy, about 3 minutes. Scrape the bowl.
Mix in drained pumpkin, egg yolk, and vanilla until combined.
Add dry ingredients to wet and stir just until no streaks remain.
Using a medium cookie scoop (about 30 g), portion dough onto prepared sheets, spacing about 2 inches apart.