Preheat oven to 350 degrees F.
In a large mixing bowl, mash bananas with a fork.
Mix in an egg, Greek yogurt, apple sauce, brown sugar, maple syrup and vanilla until well combined.
Add salt, cinnamon, nutmeg and flour and mix until well combined.
Fold in chopped walnuts.
Spray a muffin tin with nonstick cooking spray.
Scoop batter into each muffin tin until 2/3 full.
Bake for 20-22 minutes or until golden brown on top.