Preheat the oven to 350°F (175°C). Grease and flour the loaf pan or line it with parchment paper.
In a large mixing bowl, combine the grated zucchini, granulated sugar, brown sugar, vegetable oil, eggs, and vanilla extract. Mix well until combined.
In a medium bowl, whisk together the flour, baking soda, baking powder, cinnamon, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix. If using, fold in the chopped walnuts or chocolate chips.
Pour the batter into the prepared loaf pan, smoothing the top with a spatula.
Bake in the preheated oven for 50-55 minutes, or until a toothpick inserted into the center comes out clean.
Let the bread cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
For extra moisture, consider adding 1/2 cup of plain yogurt or applesauce.
Store leftover bread tightly wrapped at room temperature for up to 3 days or in the refrigerator for a week.