Preheat your oven to 350°F (175°C). Grease or line a muffin tin with liners.
In a mixing bowl, mash the ripe bananas with a fork until smooth.
Add the rolled oats, milk, honey or maple syrup, egg, and vanilla extract to the bowl with the mashed bananas. Stir well to combine.
In a separate small bowl, whisk together the baking powder, baking soda, cinnamon (if using), and salt.
Add the dry ingredients to the wet ingredients in the mixing bowl. Stir until just combined. Do not overmix.
Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full.
Bake in the preheated oven for 18-22 minutes, or until the muffins are golden brown and a toothpick inserted into the center comes out clean.
Remove the muffin tin from the oven and let the muffins cool in the tin for a few minutes before transferring them to a wire rack to cool completely.
Serve the banana oat muffins warm or at room temperature. Enjoy!