Preheat the oven to 425°F. Line a 12-cup muffin tin with paper liners or lightly grease the cups with cooking spray.

Trim the ends off the zucchini and grate it using a box grater. Place the grated zucchini in a clean kitchen towel and twist to squeeze out as much liquid as possible. Set aside.

In a large bowl, mash the bananas with a fork until mostly smooth. Add the melted butter, maple syrup, Greek yogurt, milk, eggs, and vanilla extract. Whisk until well combined. Stir in the grated zucchini.

In a separate medium bowl, whisk together the white whole wheat flour, cinnamon, baking soda, baking powder, and salt.

Pour the dry ingredients into the wet mixture. Stir gently with a spatula just until the flour is incorporated. Do not overmix; a few lumps are fine.

Divide the batter evenly among the 12 prepared muffin cups, filling each about three-quarters full.

Bake at 425°F for 5 minutes. Without opening the oven door, reduce the temperature to 350°F and continue baking for 20 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.

Remove the muffins from the oven and transfer them from the tin to a wire rack immediately. Let cool completely before storing. Keep in an airtight container at room temperature for up to 3 days, or wrap individually and freeze for up to 1 month.