Preheat oven to 350°F / 180°C and line a baking sheet with parchment paper.
Put the pumpkin puree on a plate and use paper towels to blot away some of the moisture. You want to keep blotting with fresh paper towels until the new paper towels are no longer becoming immediately saturated. This may take several paper towels, I used about 5 or 6.
Melt the butter in the microwave in 30-second increments, then pour into a mixing bowl along with the white sugar, brown sugar and blotted pumpkin puree. Mix everything together until combined.
Add the egg yolk and vanilla and mix those in until completely combined.
Add the dry ingredients to the bowl (except the oats), which includes the flour, baking powder, baking soda, salt, ground cinnamon and ground ginger. Mix everything together until totally incorporated.
Finally, add in the oats and mix them through until they are evenly distributed in the cookie dough.
Use a cookie scoop or a tablespoon to scoop out ping pong ball sized mounds of dough. Roll them into balls and place them on the baking sheet, well spaced.
Use the heel of your hand or a glass to gently squish down each cookie dough ball slightly. Bake for 14 minutes or until slightly starting to brown.
Notes
What kind of oats to use - I used quick oats for these cookies. You can also substitute for rolled oats but just know the texture will be slightly more chewy and rough. Steel-cut oats won't work in these cookies as they take too long to cook.