Preheat oven to 350°F and line a loaf pan with parchment paper and cooking spray.
In a large bowl, fold together zucchini, sugar, olive oil, Greek yogurt, eggs, lemon zest, and vanilla extract.
In a medium bowl, whisk flour, cinnamon, baking powder, salt, and baking soda. Fold dry ingredients into wet and mix until incorporated. Fold in walnuts (if using).
Pour batter into prepared pan and bake until golden brown and a toothpick inserted into the center comes out clean, rotating the pan halfway through, 45-50 minutes. Let cool in pan for 10 minutes, then remove and slice.
Meanwhile, make the glaze. Whisk all ingredients until smooth. Drizzle glaze over cooled bread and serve immediately.
Video
Notes
Storage: Store in an airtight container at room temperature or in the refrigerator for up to 4 days. You can freeze the bread for up to 3 months. Just thaw overnight in the fridge and bring to room temperature before serving.