Preheat your oven to 350°F (175°C). Grease a 9×5-inch loaf pan and lightly dust it with flour to prevent sticking.
In a large mixing bowl, whisk together the flour, granulated sugar, brown sugar, baking soda, baking powder, salt, and cinnamon until well combined.
In another bowl, whisk together the eggs, vegetable oil, and vanilla extract until smooth. Stir in the grated zucchini.
Gradually add the wet ingredients to the dry ingredients, stirring gently until just combined. Be careful not to overmix, as this can make the bread dense.
Pour the batter into the prepared loaf pan. In a small bowl, mix the cinnamon and sugar for the topping, then sprinkle it evenly over the batter.
Place the pan in the oven and bake for 50–55 minutes, or until a toothpick inserted in the center comes out clean. If the top starts to brown too quickly, loosely cover it with foil during the last 10 minutes of baking.
Allow the bread to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely before slicing.