Preheat oven to 180°C. Spray a donut pan with non-stick spray. Set aside.
Make the donuts: Whisk the flour, baking powder, baking soda, salt and cinnamon together in a medium bowl. Set aside. Whisk sugar, butter, mashed banana, vanilla, and oat milk until smooth and combined. Pour the wet ingredients into the dry ingredients and mix until just combined. Don´t overmix.
Spoon the batter into the donut pan.
Bake for 9–10 minutes until lightly browned. Allow to cool for about few minutes and transfer to a wire rack. Bake the remaining donut batter (there is enough batter for 2-3 more donuts).
Make the glaze: Place the chocolate chips, butter, syrup, and water in a medium bowl. Melt over water and stirring each time, until completely melted and smooth. Dip the donuts into the chocolate glaze. And If you like top with white chocolate.