Preheat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan with nonstick cooking spray or butter, or line it with parchment paper.
In a large mixing bowl, whisk together the 1/2 cup sugar, oil, eggs, and vanilla until smooth and well combined.
Add the flour, baking soda, baking powder, cinnamon, and salt. Stir just until no dry streaks remain. Be careful not to overmix.
Fold the shredded zucchini into the batter until evenly distributed.
In a small bowl, stir together the granulated sugar and cinnamon.
Spread half of the batter evenly into the prepared loaf pan. Sprinkle half of the cinnamon sugar mixture over the batter.
Carefully spread the remaining batter over the cinnamon sugar layer, then sprinkle the remaining cinnamon sugar evenly over the top.
Bake for 45 to 55 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs. If the top begins browning too quickly, loosely tent the loaf with foil during the last 10 to 15 minutes of baking.
Let the bread cool in the pan for 10 to 15 minutes before transferring it to a wire rack to cool completely.