Preheat oven to 350°F. Spray a 9x13-inch baking pan with non-stick cooking spray.
Grate about 2 medium zucchini to make 3 cups. Don't squeeze out the zucchini juice.
Add granulated sugar, brown sugar, cinnamon, and nutmeg in a medium bowl. Stir to combine.
Add the vegetable oil and mix until incorporated.
Add in the vanilla and the eggs one at a time. Whisk until combined and then add the next until all of the eggs have been incorporated.
In a separate bowl, add the flour, baking soda, baking powder, and salt. Stir until incorporated.
Combine the dry ingredients with the wet and beat with a hand mixer until combined.
Add the zucchini and fold in with a spatula.
Pour the batter into the prepared baking pan.
Place in the oven and let it bake for about 1 hour to 1 hour 5 minutes or until a toothpick comes out clean or with moist crumbs.
Remove from the oven and let cool completely.