Preheat oven to 350℉. Grease and flour a 9×5 loaf pan. Set aside.
Begin by combining dry ingredients. Whisk together both flours, baking powder, baking soda, salt, cinnamon, and lemon zest in a medium bowl. Set aside.
Whisk together butter and sugar in another medium bowl until smooth, then whisk in eggs and vanilla. Next, whisk in milk and sour cream until thoroughly combined. Fold in grated zucchini.
Gradually add the dry ingredients into the wet and stir until just combined. Pour into loaf pan and bake for 45-50 minutes until the edges are golden, top is firm, and a toothpick comes out clean. Let cool for at least 30 minutes before removing from pan onto a cooling rack.
To make the glaze, whisk all ingredients together until smooth. Once bread is completely cool, pour the glaze over bread and slice. Enjoy for breakfast or a snack or dessert!
*Make sure you're using whole wheat pastry flour, not regular whole wheat flour. Regular whole wheat flour will be too dense dry, and gritty in this bread. Feel free to use all all-purpose flour here if you can't find whole wheat pastry flour! This is what I use and love.
*You can substitute any milk you have on hand!
*I save the pod after removing the seeds to make vanilla bean simple syrups and to add to the pot when making oatmeal!