Preheat the oven to 375 degrees.
Grate the zucchini and set it aside. *See notes
Add the flour, salt, and baking powder to a small bowl and mix to combine. Set that aside.
In a medium bowl, add the eggs, sugar, and oil. Mix with a whisk to combine.
Zest the lemons into the egg and sugar mixture. Add the vanilla and mix to combine.
Add the grated and drained zucchini to the wet ingredients and mix well to combine.
Add the dry ingredients to the wet ingredients and gently mix everything to combine. Do not overmix. It's ok if there are some lumps left in the batter.
Add the blueberries to the batter and mix gently to combine the blueberries into the batter.
Spray a loaf pan with cooking spray and add the batter to the prepared loaf pan.
Bake the bread for 1 hour. After one hour, check for doneness by inserting a toothpick into the middle of the bread. If it comes out clean, take the loaf out of the oven. If there is still some batter left on the bread, continue baking for another 5 minutes. Repeat this process until the toothpick comes out clean.
When the bread is done, carefully take it out of the loaf pan and place it on a wire rack to cool while you make the lemon icing.