Preheat the oven to 350°F (175°C). Grease and flour a 9×5-inch loaf pan.
In a medium bowl, whisk together the flour, baking soda, baking powder, salt, cinnamon, nutmeg, ginger, and cloves until well combined.
In a large bowl, beat the granulated sugar, brown sugar, and eggs together until smooth and creamy.
Add the vegetable oil, pumpkin puree, and vanilla extract to the sugar and egg mixture. Mix until fully incorporated.
Gradually add the dry ingredients to the wet ingredients, stirring just until combined. Do not overmix.
Fold in the grated zucchini and chopped walnuts, if using, until evenly distributed.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for 55 to 60 minutes, or until a toothpick inserted into the center comes out clean.
Remove the bread from the oven and allow it to cool in the pan for 10 minutes.
Transfer the bread to a wire rack and let it cool completely before slicing.