Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with parchment paper, leaving some overhang for easy removal.
Prepare the Produce: Shred the zucchini, carrots, and apple. Place the shredded zucchini in a clean kitchen towel and squeeze firmly to remove excess moisture.
Mix the Dry Ingredients: In a large bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt until evenly combined.
Mix the Wet Ingredients: In a separate bowl, whisk together the eggs, granulated sugar, brown sugar, vegetable oil, and vanilla extract until smooth and well combined.
Combine the Batter: Add the dry ingredients to the wet ingredients and gently fold until just combined. Fold in the shredded zucchini, carrots, and apple. If using, gently fold in the chopped walnuts or pecans. Do not overmix.
Fill the Loaf Pan: Pour the batter into the prepared loaf pan and spread it evenly with a spatula. Smooth the top.
Bake: Bake for 55–65 minutes, or until the loaf is golden brown and a toothpick inserted into the center comes out clean or with a few moist crumbs. If the top browns too quickly, loosely cover it with aluminum foil.
Cool: Let the bread cool in the pan for 10–15 minutes. Carefully remove it using the parchment paper and transfer it to a wire rack. Allow it to cool before slicing and serving.