Preheat the oven to 350°F (175°C) and grease a 9x5-inch loaf pan or line it with parchment paper.
Prepare the zucchini and apple: Grate the zucchinis and apple. Squeeze out excess moisture from the grated zucchini using a clean kitchen towel or paper towels. Mix the dry ingredients: In a large bowl, whisk together the flour, baking soda, baking powder, cinnamon, and salt.
Combine the wet ingredients: In a separate bowl, whisk together the eggs, granulated sugar, brown sugar, vegetable oil (or melted butter), and vanilla extract. Stir in the grated zucchini and apple. Combine wet and dry ingredients: Gradually fold the dry ingredients into the wet mixture, stirring gently until just combined. Avoid overmixing to ensure a light, fluffy texture.
Add optional mix-ins: If you’re using walnuts or pecans, fold them into the batter now.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean or with just a few crumbs attached. If the top starts to brown too quickly, cover it loosely with aluminum foil. Cool in the pan for 10 minutes before transferring the loaf to a wire rack to cool completely.
Serve once fully cooled and enjoy!