Preheat Your Oven and Prepare Loaf Pan: Preheat your oven to 350°F (175°C). Grease a 9x5 inch loaf pan or line it with parchment paper.

Drain the Zucchini: If your grated zucchini is very wet, you might want to squeeze out a little bit of the moisture using a clean kitchen towel or a few paper towels.

Mix Wet Ingredients: In a large bowl, combine the sourdough discard, grated zucchini, eggs, vegetable oil, both sugars, and vanilla extract. Stir until well mixed.

Combine the Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, baking powder, salt, cinnamon, and nutmeg.

Combine Wet and Dry Mixtures: Gradually add the dry ingredients to the wet ingredients, stirring until just combined. If you're using walnuts or chocolate chips, fold them in at this stage.

Pour into Pan and Bake: Pour the batter into the prepared loaf pan. Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean.

Cool and Serve: Allow the bread to cool in the pan for about 10 minutes, then remove it from the pan and let it cool completely on a wire rack.