Preheat the oven to 350°F (175°C). Grease or line a loaf pan with parchment paper.
Mix dry ingredients: In a large bowl, whisk together gluten-free flour, baking soda, baking powder, cinnamon, and salt.
Combine wet ingredients: In a medium bowl, whisk together sugar, oil, eggs, and vanilla extract until smooth and combined.
Add zucchini: Stir the grated zucchini into the wet mixture, ensuring it is well incorporated.
Combine wet and dry: Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Add extras: If using, fold in the walnuts or chocolate chips.
Bake: Pour the batter into the prepared loaf pan and bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean.
Cool: Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.