Preheat oven to 350 degrees F. Gently spritz a 6-cavity donut pan with cooking spray and set aside.
In a medium bowl, whisk together the oat flour, baking powder, baking soda, pumpkin pie spice, and salt.
In a small bowl, whisk together the cornstarch and water. Set aside.
In another bowl, whisk together the pumpkin purée, coconut sugar, milk, vanilla extract, apple cider vinegar, and cornstarch slurry.
Stir the dry ingredients into the wet ingredients until just combined.
Fill the donut cavities using either a piping bag** or a spoon.
Bake for 8 to 10 minutes until set.
Let cool in the pan on a cooling rack for 5 minutes. Turn the donuts out onto the cooling rack and let them completely cool.