Preheat oven to 350°F (175°C) and grease a standard 12-cup muffin tin or line with paper liners.
In a large mixing bowl, combine the mashed bananas, Greek yogurt, egg, maple syrup, and vanilla extract; whisk until thoroughly integrated.
In a separate bowl, whisk together the whole wheat flour, baking soda, baking powder, cinnamon, and salt.
Gradually fold the dry ingredients into the wet ingredients using a spatula until just combined; do not overmix.
Distribute the batter evenly among the 12 muffin cups, filling each about three-quarters full.
Bake for 18 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Cool the muffins in the tin for 5 minutes, then transfer to a wire rack to cool completely.