Preheat oven to 350F with the rack in the center position. Prep a muffin tin* with cooking spray or paper liners.
Put the oats in a dry, clean blender. Pulse briefly to grind to a flour consistency. Combine the oat flour, baking soda, baking powder, salt, sugar, and cinnamon in a medium mixing bowl. Set aside.
Add the milk, oil, egg, banana, and vanilla to the blender and puree until smooth. Add the wet mixture to the dry ingredients and mix until combined. Let sit 10 minutes to ensure the best rise.
Fold in the blueberries (or add them on top of the batter once inside the muffin tin). Pour the batter into the wells of the muffin tin about ¾ full.
Bake until lightly brown and a golden crust forms around the edges, 20-22 minutes in a standard muffin tin (about 12 minutes in a mini muffin tin).
Allow the muffins to cool in the pan not longer than 5 minutes - just until you can touch them. Remove muffins and allow to cool on a cooling rack. Serve warm if possible but room temperature is OK.