Preheat oven to 350 degrees F. Spray a loaf pan with cooking spray, and set aside.
Add melted butter to a large mixing bowl. (I actually melt my butter in the microwave in the mixing bowl.) Whisk in pumpkin and sugar until smooth.
Add eggs, vanilla, cinnamon, and cloves. Whisk again until smooth. Put away your whisk, and stir in zucchini with a mixing spatula or spoon.
Add flours, baking soda, and salt. Stir just until dry ingredients are incorporated. Do not overmix.
Spread dough evenly into prepared pan. Bake in preheated oven for 50-60 minutes or until toothpick inserted into center of loaf comes out mostly clean. Allow to cool at least 10 minutes before removing from pan and slicing.
You can use all white or gluten-free flour in this recipe if desired.