Preheat the oven to 350°F (175°C) and grease a muffin tin or line with muffin liners.

In a mixing bowl, mash the ripe bananas until smooth.

Add the grated zucchini, honey, egg, applesauce, and vanilla extract to the mashed bananas. Mix well.

In another bowl, combine the whole wheat flour, baking soda, baking powder, salt, and cinnamon.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Fold in the walnuts if using.

Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.

Allow muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.