Start by preheating your oven to 350ºF and lightly spray a 13x9 baking pan with nonstick cooking spray.
Next, whisk the flour, xanthan gum, salt, baking powder, baking soda, cinnamon, cocoa powder and the sugar together in a large mixing bowl.
Once the dry ingredients are mixed together, add the eggs, butter and vanilla extract, and mix until well combined.
Finally, add the shredded zucchini and chopped walnuts, using a spatula to fold them into the cake batter until well mixed. Be sure to stop and scrape the sides and bottom of the bowl into the batter every now and again as you fold.
Once everything is mixed together well, spread the chocolate cake batter into the baking dish that you greased up in the first step.
Bake the cake for about 50-60 minutes at 350ºF, or until a toothpick or cake tester inserted into the center of the cake comes out clean.
Once it has completely cooled, your gluten-free chocolate zucchini cake is ready to serve and enjoy! I like to dust mine with a little bit of powdered sugar followed by a big dollop of whipped cream on top.