Preheat oven to 350°F (180°C). Spray an 8½x4½-inch loaf pan with baking spray with flour. Line pan with parchment paper, letting excess extend over all sides of pan.

In a large bowl, whisk together sugars, oil, eggs, and vanilla until well combined. Stir in zucchini.

In a medium bowl, whisk together flour, baking powder, salt, and cinnamon. Gradually fold flour mixture into sugar mixture until moistened and combined. Spoon batter into prepared pan; smooth into an even layer with a small offset spatula or the back of a spoon. Tap pan on a kitchen towel-lined counter several times to settle batter.

Bake until a wooden pick inserted in center comes out clean and an instant-read thermometer inserted in center registers at least 205°F (96°C), about 1 hour and 15 minutes. Let cool in pan for 10 minutes. Using excess parchment as handles, remove from pan, and let cool completely on a wire rack.