Preheat oven to 350°F (175°C). Grease a 9×5-inch loaf pan and line with parchment paper.,In a medium bowl, whisk together flour, baking powder, baking soda, and salt.,In a large bowl, whisk together eggs, sugar, oil, lemon zest, lemon juice, and vanilla until smooth.,Stir in the grated zucchini.,Add the dry ingredients to the wet mixture and stir until just combined. Fold in poppy seeds or nuts if using.,Pour batter into prepared pan and smooth the top.,Bake for 50–60 minutes or until a toothpick inserted into the center comes out clean.,Cool in the pan for 10–15 minutes, then transfer to a wire rack to cool completely.,For the glaze: whisk powdered sugar and lemon juice until smooth. Drizzle over cooled bread.