Preheat oven to 375 degrees F (190 degrees C).
Blend oats into a flour and combine in a bowl with baking powder, baking soda, salt, and cinnamon.
Blend milk, spinach, vanilla and oil, egg, and banana until combined.
Pour the spinach mixture on top of dry ingredients and stir until combined. Do not overmix the batter, just mix it enough until it is all incorporated.
Pour into a mini muffin pan and bake at 375 degrees F for about 15 minutes or until a toothpick inserted comes out clean.
Remove from the oven and allow the muffins to cool for at least 5 minutes before removing them from the silicone pan. Transfer to a wire rack to fully cool.
