Preheat Oven: Set your oven to 350°F (175°C) and grease a 9x5-inch loaf pan, or line it with parchment paper.
Prepare Zucchini: Grate the zucchini, then lightly squeeze it in a clean towel or paper towels to remove excess moisture. Set it aside.
Mix Dry Ingredients: In a large bowl, whisk together the flour, oats, baking soda, baking powder, cinnamon, and salt.
Mix Dry Ingredients: In a large bowl, whisk together the flour, oats, baking soda, baking powder, cinnamon, and salt.
Combine Wet Ingredients: In another bowl, whisk the eggs, then add the sugar, oil, and vanilla extract. Stir until well mixed.
Add Zucchini: Fold the grated zucchini into the wet ingredients.
Combine Wet and Dry: Gradually mix the dry ingredients into the wet ingredients until just combined. Be careful not to overmix. If using, fold in walnuts or chocolate chips.
Pour and Bake: Pour the batter into the prepared loaf pan and smooth the top. Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean.
Cool: Allow the bread to cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.