Preheat oven to 350° (325° for dark pans) and generously spray loaf pan(s) with oil. Toss the grated zucchini into the bowl of a mixer, pouring the following ingredients on top. Sugar, oil, yogurt, egg, lemon zest, and lemon juice.
Will be "soupy" so mix on low until all ingredients are mixed in. Meanwhile, in a separate bowl, add flour, whole wheat flour, baking soda, baking powder, and salt, whisk gently to combine.
Add to liquid ingredients while mixer is on stir or lowest setting, careful to not floof flour all over. Scrape down sides, mix one more time.
Using a spatula, scrape the collected zucchini off the beater and mix into batter by hand. If making one large loaf, scoop batter into prepared loaf pan. If making mini loaves, evenly distribute batter between prepared pans.
Bake large loaf 50-60 minutes; mini loaves 25-35 minutes until golden and toothpick inserted in center comes out clean. Cool on wire rack in pans for 10 minutes.
Remove from pans (slide a knife around edges if needed to encourage loaf(s) onto cooling rack, turn upside down and tap gently on bottom to release from pan)
Finish cooling entirely on wire rack, you may turn the bread right side up after removing from pans if you don't want the pattern of the rack on the top of the loaf. Once cooled, prepare glaze.
Mix powdered sugar and 1 tablespoon of lemon juice together until spreadable but not too thin, if needed to thin out a bit, add a little lemon juice at a time until desired consistency.
Place a sheet of wax paper under the cooling rack prior to pouring glaze, this will catch all of your drips. Drizzle glaze all over bread loaf, mostly centered, using back of spoon gently move some glaze to the edges so that some drizzles down the sides of the loaf.
If desired, wrap in parchment paper, plastic wrap or place in zip lock bag. Enjoy!