Heat the oven to 350° F.
Line the long sides of a 9x5" loaf pan with a piece of parchment paper. Spray inside the short sides of the pan with cooking spray.
Trim the ends off the zucchini. Lay cheesecloth (or a thin towel) down on a cutting board, then place a box grater on the middle of the cheesecloth. Grate the zucchini using the large holds of the box grater or with the shredding disc in a food processor. If using a food processor, add the grated zucchini to the middle of the cheesecloth.
Gather up the cheesecloth to create a bundle holding the grated zucchini. Hold it over the sink and squeeze and twist the bundle as tightly as possible to extract as much water as you can. When you think you're done, give it a few more good twists to make sure. Measure out 1½ cups and set the zucchini aside.
In a large bowl, whisk the almond flour, arrowroot, cinnamon, baking soda and salt.
In a medium bowl, whisk the eggs, honey, lemon zest, lemon juice and vanilla.
Stir the wet ingredients into the dry ingredients with a spatula until no more almond flour is visible. The batter will be thick. Add the grated zucchini (and any optional add-ins) and stir until it's evenly distributed throughout the batter.
Pour or scoop the batter into the prepared loaf pan and smooth the top. Bake for 50-55 minutes, until golden brown on top and a toothpick inserted in the middle comes out without any raw batter attached (some crumbs are fine). Let cool completely, then slice and serve.