Preheat the oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan, or line it with parchment paper for easy removal.
Prepare the zucchini: Grate the zucchini with a box grater or food processor. After grating, place the zucchini into a clean kitchen towel and squeeze out any excess moisture. Set it aside.
Mix dry ingredients: In a medium mixing bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt. Set aside.
Mix wet ingredients: In a large bowl, beat the eggs, then add the melted butter, sugar, and vanilla extract. Stir well until fully combined.
Combine wet and dry ingredients: Gradually add the dry ingredients to the wet mixture, stirring just until incorporated.
Fold in zucchini: Add the grated zucchini to the batter and fold it in gently, followed by the nuts or chocolate chips if you're using them.
Bake: Pour the batter into the prepared loaf pan and spread it evenly. Bake for 60-70 minutes, or until a toothpick inserted into the center of the loaf comes out clean. If the bread begins to brown too quickly, loosely cover it with aluminum foil halfway through baking.
Cool and serve: Let the zucchini bread cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely. Slice and enjoy!