Preheat the oven to 350 degrees Fahrenheit (177 degrees Celsius). Grease your baking pan of choice
Whisk the flour, baking powder, baking soda, salt, cinnamon, nutmeg, and walnuts together in a large bowl until combined. Set aside.
Whisk oil, brown sugar, granulated sugar, egg, vanilla, and zucchini together until combined in a medium bowl.
Pour the wet ingredients into a the dry ingredients. Gently whisk until "just" combined. Do not over-mix.
Spread the batter into prepared pan. Bake for 45-55 minutes. You will need to adjust the baking time if you're baking muffins. The bread is done when a toothpick inserted in the center comes out mostly clean with no raw batter.
Remove the bread from the oven and set on a wire rack. Allow to cool completely before slicing.