Preheat oven to 350°F (175°C) and line a muffin tin with liners.
Grate zucchini and squeeze out excess moisture using a clean towel.
In a bowl, whisk flour, baking soda, baking powder, salt, and cinnamon.
In a separate large bowl, mash bananas and mix with zucchini, sugar, oil, eggs, and vanilla.
Add dry ingredients into wet ingredients and stir until just combined. Do not overmix.
Fold in chocolate chips or nuts if using.
Fill muffin cups ¾ full with batter.
Bake for 18–22 minutes or until a toothpick comes out clean.
Cool for 10 minutes before transferring to a wire rack.