In a large bowl combine dry ingredients, which are rice flour, gluten-free oat flour, potato starch, baking powder, baking soda, brown sugar, and cinnamon.
In a separate bowl combine mashed banana, soy milk, melted vegan butter, vinegar, and vanilla extract.
Add in wet ingredients into the dry and combine well. The batter should be really fluffy and soft.
Grease your donut pan with vegan butter and pour in the prepared batter.
Bake at 150°C (300F) for 15 minutes.
In a smaller bowl combine sugar and cinnamon and melt the vegan butter.
After baking, carefully brush donuts with vegan butter and cover each donut in cinnamon sugar. Enjoy!