Preheat Oven and Grease the Loaf Pans - Preheat the oven to 350 degrees Fahrenheit. Spray both loaf pans with cooking spray.
Peel and Shred the Zucchini - Thoroughly wash your zucchini. Use a vegetable peeler to remove the skin. Then, use a vegetable grater to shred your zucchini, removing the seeds if they are large.
Combine the Dry Ingredients - In a medium mixing bowl, combine the flour, baking powder, baking soda, salt, nutmeg, and cinnamon.
Combine Sugar, Butter, Vanilla, and Eggs - In a large mixing bowl, combine the sugar, butter, eggs, and vanilla using an electric mixer. Beat at medium speed until smooth, scraping the sides of the bowl as needed.
Add the Dry Ingredients to the Wet ones - Gently add the dry ingredients into the wet ingredients. Beat the mixture at low speed until combined. The mixture will be thick.
Add the Zucchini - Using a rubber spatula, gently fold the shredded zucchini into the mixture. If desired, fold the chopped walnuts into the mixture as well.
Bake the Bread - Evenly four the batter into the two loaf pans. Bake for 55-65 minutes, inserting a toothpick to see if it is done. If it comes out clean, the bread is done, if there are crumbs or batter, continue to bake.
Allow the bread to cool for 10 minutes in the pans. Afterward, transfer to a wire rack so they can completely cool.