Preheat the oven to 350°F. Lightly coat a 9x5-inch loaf pan with nonstick cooking spray.
In a large mixing bowl, mash the bananas until mostly smooth.
Add the egg, maple syrup, Greek yogurt, vanilla extract, and cooled melted butter. Stir until well combined.
Add the whole wheat flour, baking soda, baking powder, cinnamon, and salt. Stir just until combined, being careful not to overmix.
Pour the batter into the prepared loaf pan and spread it into an even layer.
Bake for 45–55 minutes, or until a toothpick inserted into the center comes out clean.
Begin checking the bread after 35 minutes. If the top is browning too quickly, loosely tent it with aluminum foil and continue baking.
Let the bread cool in the pan for 10–15 minutes, then carefully transfer it to a wire rack to cool completely before slicing and serving.
Notes
For the best results, make sure that all the ingredients are at room temperature for mixing together for this recipe. You can use a high quality coconut oil, canola oil or vegetable oil instead of the butter if you prefer. Store any leftover bread at room temperature in an airtight container for up to 1 week.