Preheat the Oven:
Preheat your oven to 350°F (176°C) and grease a 9” x 5” loaf pan. Line with parchment paper for easy removal.
Prepare the Zucchini:
Grate the zucchini using a box grater or food processor. Squeeze out excess water using a clean kitchen towel or paper towels.
Mix the Dry Ingredients:
In a medium mixing bowl, whisk together the flour, baking soda, baking powder, salt, and cinnamon.
Mix the Wet Ingredients:
In a large mixing bowl, whisk the sourdough starter discard, eggs, oil, and brown sugar until smooth and well combined.
Combine and Fold in Ingredients:
Gradually add the dry ingredients to the wet mixture, folding gently to combine. Be careful not to overmix. Fold in the prepared zucchini and any optional add-ins like walnuts or chocolate chips.
Bake the Bread:
Pour the batter into the prepared loaf pan, smoothing the top with a spatula. Bake in the preheated oven for 55–60 minutes, or until a toothpick inserted into the center comes out clean.
Cool and Serve:
Allow the bread to cool in the pan for 15 minutes before transferring it to a wire rack to cool completely. Slice and enjoy!