Preheat your oven to 350°F (175°C). Grease a loaf pan.
In a large bowl, whisk together the flour, sugar, brown sugar, baking powder, baking soda, salt, and cinnamon.
In another bowl, mix the grated zucchini, vegetable oil, and vanilla extract.
Add the wet ingredients to the dry ingredients and stir until just combined. Do not overmix.
Fold in the chopped walnuts if using.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 60 minutes, or until a toothpick inserted into the center comes out clean.
Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.