In a large bowl mash the bananas well until they are glossy.
Add the melted butter, egg, greek yogurt, maple syrup, and vanilla and stir until combined well with the bananas.
Add baking soda, salt, cinnamon and flour to the wet ingredients and mix until combined.
Bake at 350 degrees for 12 to 15 minutes.
Let the muffins cool in the pan for 5 minutes and then transfer to a wire rack.
Notes
Use ripe bananas with a lot of brown spots for sweet muffins! If your bananas are not overripe, feel free to up maple sugar to ⅓ cup if you like a sweeter muffin.