Preheat oven to 350°F (177°C). Spray a 9x5-inch loaf pan with nonstick cooking spray, line with parchment paper for easier removal if desired, and set aside.
In a large mixing bowl, whisk together the flour, cinnamon, baking powder, baking soda, nutmeg, and salt until well combined. Set aside.
In a separate mixing bowl whisk together the oil, brown sugar, granulated sugar, eggs, and vanilla extract until well combined. Stir in the shredded zucchini.
Combine the wet ingredients and dry ingredients and mix until just combined, then gently fold in the chopped walnuts. Pour the batter into the prepared loaf pan and spread into one even layer.
Bake at 350°F (177°C) for 45-55 minutes or until a toothpick inserted into the center comes out clean.
Remove from the oven and cool in the pan on a wire rack for 20 minutes, carefully remove from the pan, and place on the wire rack to finish cooling. Once cooled, slice into pieces and enjoy!