Preheat the oven to 350°F (175°C). Grease and flour two 8x4-inch loaf pans or line them with parchment paper.
Wash and grate the zucchini using a box grater. Measure 2 cups. Do not squeeze it dry unless it is extremely watery.
In a medium bowl, whisk together the flour, baking soda, baking powder, salt, and cinnamon.
In a large bowl, whisk together the eggs, vegetable oil, sugar, and vanilla until well combined.
Gradually add the dry ingredients to the wet ingredients. Stir gently just until combined. Do not overmix.
Fold the grated zucchini into the batter until evenly distributed.
If using walnuts or pecans, gently fold them into the batter.
Fill the pans.
Divide the batter evenly between the prepared loaf pans and smooth the tops.
Bake for 50–60 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Let the loaves cool in their pans for 10–15 minutes. Transfer to a wire rack and allow them to cool for at least 20–30 minutes before slicing.
