Preheat your oven to 350°F. Grease a 12-cup muffin pan or line with paper liners.
In a medium bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt.
In a separate, larger bowl, combine the mashed bananas, sugar, oil, eggs, and vanilla extract until fully combined. Stir in the zucchini.
Pour the dry ingredients into the wet ingredients and stir until just combined- do not overmix.
Divide the batter between the muffin liners, filling to the very top.
Bake for 22-26 minutes until the tops are golden, and a toothpick inserted into the center comes out clean.
Let the muffins cool in the pan for 10 minutes, then move them to a wire rack to cool completely.