Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line with parchment. In a medium bowl, whisk together flour, baking soda, baking powder, salt, cinnamon, and nutmeg.

In a large bowl, whisk oil, both sugars, applesauce, and vanilla until smooth. Stir in the grated zucchini.

Add dry ingredients to wet and fold with a spatula just until no flour streaks remain. Pour into the prepared pan and smooth the top. Sprinkle with coarse sugar if desired.

Bake 50 to 55 minutes, until a toothpick comes out with moist crumbs. Cool in the pan 10 minutes, then transfer to a wire rack and cool completely before slicing.