Preheat oven to 350°F (175°C). Lightly grease or line an 8x4-inch loaf pan.
Mix dry ingredients in a bowl: flour, baking soda, baking powder, cinnamon, and salt.
In a separate bowl, whisk wet ingredients: sourdough discard, eggs, oil, brown sugar, and vanilla.
Combine wet and dry mixtures until just mixed.
Fold in grated zucchini and any optional add-ins like chocolate chips.
Pour batter into prepared loaf pan. Smooth the top.
Bake for 50–60 minutes, or until a toothpick comes out mostly clean.
Let it cool in the pan for 10 minutes, then move to a wire rack to cool completely.