Preheat oven to 350 degrees F. Grease 12 muffin tins or line with paper liners.
In a large bowl, stir together the mashed bananas, egg, greek yogurt, coconut oil, brown sugar, maple syrup, and vanilla until well combined.
In a medium bowl, whisk together baking soda, salt, cinnamon, and flour. Add to wet ingredients, stirring until just combined. Gently fold in walnuts.
Scoop batter into muffin tins, evenly distributing batter. Bake in preheated oven for about 18-20 minutes, until a toothpick inserted in the center comes out clean. Let cool before serving.
Notes
For the freezer: Freeze in an airtight ziplock bag after freezing. Allow to thaw at room temperature when ready for use.