Preheat your oven to 350°F (175°C). Grease and flour two 8x4-inch loaf pans.
In a large bowl, whisk together the brown sugar, granulated sugar, oil, eggs, and vanilla until smooth.
Fold in the grated zucchini.
In another bowl, combine the flour, baking soda, baking powder, salt, cinnamon, and nutmeg.
Slowly add the dry ingredients to the wet mixture, stirring just until combined. Don’t overmix.
Fold in the nuts if using.
Divide the batter evenly between the prepared loaf pans.
Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean.
Let the loaves cool in the pans for 10 minutes, then remove and place on a wire rack to cool completely.