Preheat oven to 350 degrees Fahrenheit. Grease and flour two 8-inch round cake pans.
With an electric mixer, beat the eggs, oil, sugar, vanilla, lemon zest, and juice until blended. Fold in the zucchini.
In a small bowl, whisk together the flour, salt, baking powder, and baking soda. Add the dry ingredients to the wet mixture in batches, mixing to blend. Gently fold in the blueberries. Divide the batter evenly between the cake pans.
Bake 40-45 minutes or until a toothpick inserted in the center of a cake comes out clean. Cool in pans for 10 minutes then invert onto a wire rack to cool completely. Using a serrated knife cut off the cake dome. You want an even surface or your frosting is going to run right off the cake.
Frosting & Topping (optional)
Beat together the cream cheese and butter until smooth. Add powdered sugar, salt, vanilla, and lemon juice. Mix on low until sugar is well incorporated, then turn the mixer to high. Beat for 2-3 minutes then add more lemon juice if you’d like softer frosting.
Slice zucchini lengthwise into thin strips using a mandoline slicer.
In a small saucepan bring water and sugar to a boil, stirring until sugar dissolves. Add zucchini strips. Reduce heat to medium and simmer, until zucchini is translucent, 15 to 20 minutes. (Placing a round piece of parchment paper on top of zucchini will keep them submerged).
Let zucchini cool in syrup. Arrange zucchini in a single layer on a wire rack set over a baking sheet. Let dry for 30-60 minutes.
Layer the cakes and frosting then garnish with blueberries, candied zucchini, and lemon if desired.