Place grated zucchini in a colander while you are getting other ingredients ready. Preheat oven to 375ºF and line an 8 x 8 baking dish with unbleached parchment paper.
In a large bowl, add egg, oil, maple syrup and pure vanilla extract; whisk to combine. Add cacao powder, baking soda, and salt; whisk until well mixed.
Give zucchini a gentle squeeze but do not ring out completely; add to bowl and stir. Add flour and mix gently until combined.
Transfer batter into the prepared baking dish and level with spatula. Bake for 25-28 minutes or until the center is barely jiggly. Do not over-bake as brownies will have more of a cake consistency. A toothpick inserted has to come out somewhat clean, but not completely clean. If center is too jiggly, bake a bit more – ovens vary.
Remove from the oven and let cool for about an hour. Lift by the parchment paper flaps and transfer to a cooling rack to cool off completely. Cut into 16 squares.
Store in a glass airtight container in a cool, dry place for up to 4 days. You can refrigerate for up to a week, and freeze for up to 3 – 4 months.