Preheat your oven to 350°F (175°C) and line or grease a muffin tin.
In a large bowl, mash the bananas until mostly smooth.
Stir in Greek yogurt, honey or maple syrup, egg, and vanilla extract.
Add the flour, oats, baking soda, salt, and cinnamon. Mix just until combined—don’t overdo it.
Scoop the batter evenly into the muffin tin (about 3/4 full each).
Bake for 18–22 minutes, or until a toothpick comes out clean.
Let them cool in the tin for 5 minutes before transferring to a wire rack.