Preheat the oven to 350°F (175°C). Grease and flour the loaf pan or line it with parchment paper.
In a large mixing bowl, combine the grated zucchini, pumpkin puree, eggs, vegetable oil, granulated sugar, and brown sugar. Whisk until well mixed.
In another bowl, sift together the flour, cocoa powder, baking soda, baking powder, spices (cinnamon, nutmeg, ginger, and cloves), and salt.
Gradually add the dry ingredients to the wet mixture, stirring with a rubber spatula until just combined. Do not over-mix.
Gently fold in the chocolate chips and nuts (if using) until evenly distributed.
Pour the batter into the prepared loaf pan and spread it out evenly.
Bake in the preheated oven for about 60 minutes, or until a toothpick inserted into the center comes out clean.
Once done, remove from the oven and let it cool in the pan for about 10 minutes. Then transfer to a wire rack to cool completely before slicing.