Preheat the oven to 350°F and generously grease a nonstick bundt pan with cooking spray.
In a large mixing bowl, whisk together the flour, brown sugar, baking powder, baking soda, pumpkin pie spice and salt.
Add the pumpkin puree, eggs, oat milk, vanilla extract, maple syrup and coconut oil to the dry ingredients and whisk together until a smooth batter forms, about 30 seconds.
Pour the batter into the prepared pan and smooth into an even layer.
Bake in the center rack of the oven for 60-65 minutes or until a toothpick inserted into the center comes out clean.
Transfer the pan to a wire rack to cool for 15 minutes before flipping it over to remove the cake from the pan. Let cool fully for 1 hour before slicing and serving.