Preheat the oven to 350 degrees F and spray a donut pan with non-stick spray.
Whisk the flour, brown sugar, baking powder, pumpkin pie spice and salt in a large bowl.
Pour in the melted vegan butter, pumpkin puree, oat milk and vanilla. Mix well with a large spoon until combined.
Spoon the batter into the donut pan to the top of each cavity(or use a piping bag for less mess).
Place into the oven and bake for 10-12 minutes, or until the edges are slightly browned and the donuts spring back when touched. This will largely depend on the size of your donut pan.
Make the maple glaze - In a medium bowl, whisk all glaze ingredients together until a glaze is formed. If it's too thick, add a teaspoon of oat milk at a time until you reach the desired consistency. I think the perfect consistency is runny like corn syrup, but you can make it thicker and spoon it on top if desired.
Dip the slightly cooled donuts in the glaze, then place on a wire rack (with parchment paper underneath to catch drippings). Enjoy right away or let the glaze harden for 15 minutes or so.