Preheat oven to 350°F. Spray two 9”x 5” bread pans with baking spray and line with parchment paper. Set aside.
In a separate bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.
3 ½ cups all-purpose flour, 1 ½ teaspoons baking powder, 1 teaspoon baking soda, 1 teaspoon kosher salt, 1 Tablespoon ground cinnamon, ½ teaspoon ground nutmeg
In a large bowl, beat the granulated sugar, brown sugar, eggs, oil, and vanilla extract together using an electric mixer. Mix in the grated zucchini and mashed banana until combined.
¾ cup granulated sugar, ⅔ cup light brown sugar, 3 large eggs, ¾ cup vegetable oil, 2 teaspoons vanilla extract, 2 cups grated zucchini, 1 cup mashed banana
Add the dry ingredients to the wet mixture. Use a spatula to fold it in gently until just combined — don’t overmix.
Divide the batter evenly between the prepared pans. If using the cinnamon sugar topping, sprinkle it generously over the top of each loaf.
½ cup white sugar, 1 teaspoon ground cinnamon
Bake for about 45 minutes, or until a toothpick inserted into the center comes out clean. Let the mixture cool in the pan for 10–15 minutes, then transfer it to a wire rack to cool completely.