Grate zucchini using a box grater or food processor to yield 2 cups. Squeeze out excess moisture using a clean kitchen towel or cheesecloth to prevent a soggy bread texture.

Preheat oven to 350°F (175°C) and grease a 9×5-inch loaf pan. In a large bowl, whisk together granulated sugar, brown sugar, and oil. Add eggs and vanilla extract, mixing until smooth. Stir in the grated zucchini.

In a separate bowl, whisk together flour, baking powder, baking soda, salt, and ground cinnamon. Gradually add dry ingredients to the wet mixture, stirring until just combined. Avoid overmixing.

In a small bowl, mix granulated sugar and cinnamon. Set aside for sprinkling over the batter.

Pour the batter into the prepared loaf pan and smooth the top. Sprinkle the cinnamon-sugar topping evenly over the batter. Bake for 50-60 minutes or until a toothpick inserted in the center comes out clean. Tent with foil if browning too quickly.

Cool in the pan for 10-15 minutes before transferring to a wire rack to cool completely. Slice and serve with butter or cream cheese for extra flavor.