Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper for easy removal.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon. Set aside.
In a large bowl, combine the granulated sugar, brown sugar, and vegetable oil. Mix until well combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract, grated zucchini, lemon zest, and lemon juice until just combined.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix. If using, fold in the chopped nuts.
Pour the batter into the prepared loaf pan and smooth the top. Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
While the bread is baking, prepare the glaze by whisking together the powdered sugar, lemon juice, and lemon zest in a small bowl until smooth.
Once the bread is done, let it cool in the pan for 10 minutes before transferring it to a wire rack to cool completely. Drizzle the glaze over the cooled bread before slicing.