Preheat your oven to 350°F. Line your 9x5 loaf pan with parchment paper so it overhangs on the two long sides — this creates handles for lifting the bread out later. Spray the parchment lightly with cooking spray. Grate your zucchini using the large holes of a box grater, measure 1 packed cup, and set it aside.
Whisk the wet ingredients: In your large mixing bowl, crack the 3 room-temperature eggs and whisk them well. Add the maple syrup, baking powder, baking soda, vanilla extract, cinnamon, and salt. Whisk again until everything is smooth and uniform. I always whisk the leaveners into the wet ingredients first — it ensures they are evenly dispersed without overmixing the dry ingredients later. The mixture should be pale, glossy, and slightly thickened.
Fold in the zucchini: Add the packed cup of grated zucchini to the bowl and fold it in gently with your spatula. You'll see the bright green flecks start to lace through the golden batter.
Add the almond flour: Measure the almond flour carefully by spooning it into your measuring cup and skimming the top level with a knife. Add it to the bowl and fold gently with your spatula just until no dry streaks remain. The batter will be thick, rustic, and incredibly fragrant. Don't overmix — it's fine if it looks a little rustic.
Bake: Pour the batter into your prepared loaf pan and spread it even. Bake for 50 minutes. Start checking at 45 minutes — a toothpick inserted into the center should come out clean or with just a few moist crumbs. If the top is browning too fast around minute 40, tent it loosely with foil.
Cool and slice: Remove the bread from the oven and let it cool in the pan on a rack for 10 minutes. Then, holding the parchment handles, lift the bread out of the pan and let it cool completely on the rack, about 30 to 60 minutes. I know the wait is hard, but slicing while it's warm will make the tender crumb crumble. Use a sharp serrated knife and a gentle sawing motion for neat, bakery-style slices.