Preheat oven to 350 degrees. Sift oat flour, cocoa powder, baking powder, baking soda and salt into a large mixing bowl. In a separate mixing bowl, use a hand mixer to beat avocado and egg, until smooth. Add sugar or stevia and beat until smooth. Once fluffy, whisk in milk and vanilla extract until incorporated. Pour wet mixture into dry ingredients while beating on low. Increase the mixed speed to medium and beat until well incorporated. Use a spatula to stir in any remaining dry mixture on the sides or bottom of the bowl. Coat a donut baking pan with cooking spray. Pour batter into each donut well about ¾ of the way to the top (about ¼ cup in each), but not covering the donut hole center. Bake for 13-15 minutes, until toothpick inserted into the center comes out clean. Remove from oven and allow to slightly cool. Flip them onto a baking sheet fitted with a wire rack. In a small bowl, microwave dark cacao for 30 seconds on high. Stir until fully melted. Use hand mixer to beat in avocado on high until very smooth, then beat in milk. Pour a tablespoon of glaze onto each donut. Top with nuts and/or coconut and serve.