Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or lightly grease it with cooking spray.
In a large bowl, mash the ripe bananas until smooth and creamy.
Add the egg, honey (or maple syrup), milk, vanilla extract, and melted coconut oil (or butter) to the mashed bananas. Whisk until well combined.
In a separate bowl, whisk together the oats, flour, baking powder, baking soda, cinnamon (if using), and salt.
Gradually fold the dry ingredients into the wet mixture until just combined. Avoid overmixing to keep the muffins light and fluffy.
Divide the batter evenly among the prepared muffin cups, filling each about three-quarters full.
Bake for 18-20 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.