Prepare the oven: Preheat the oven to 350°F (175°C). Grease a loaf pan or line it with parchment paper.
Prepare the zucchini: Grate the zucchini and gently squeeze out some excess moisture.
Mix the wet ingredients: In a large bowl combine the mashed bananas, eggs, vegetable oil, vanilla extract, white sugar, and brown sugar.
Combine the dry ingredients: In another bowl whisk together flour, baking soda, baking powder, salt, and cinnamon.
Mix the batter: Gradually add the dry ingredients to the wet mixture and stir until just combined.
Add mix-ins: Fold in the grated zucchini, dried cranberries, and chopped walnuts.
Transfer to pan: Pour the batter into the prepared loaf pan and spread evenly.
Bake the bread: Bake for 55–65 minutes, or until a toothpick inserted in the center comes out clean.
Cool before slicing: Allow the bread to cool in the pan for about 10 minutes, then transfer to a rack to cool completely.