Preheat your oven to 350 degrees F. Grease an 8x4x2 loaf pan with cooking spray.
To shred your zucchini, first rinse the zucchini and pat it dry. Trim off and discard the ends. Shred the zucchini in a food processor or using a box grater, until you have enough to measure one cup.
For the lemon zest, rinse and pat dry two lemons. Use a lemon zester to scrape the lemon peel until you have one tablespoon.
Add your shredded zucchini and lemon zest to a large mixing bowl. Add in the sugar, oil, egg and lemon extract. Stir until mixed.
In a small mixing bowl, add your flour, cinnamon, baking soda, salt and baking powder. Whisk them to blend.
Add your flour mixture to your large bowl with the zucchini batter. Gently stir to combine. Chop up some shelled walnuts until you have ½ cup. Stir the chopped walnuts into your batter.
Transfer the batter to your loaf pan and bake, uncovered, for 50-55 minutes, or until a toothpick inserted in the center comes out clean. Let the pan rest for ten minutes on a wire rack before inverting the zucchini bread onto a cooling rack (wear oven mitts.) Flip the zucchini bread over so that it is right-side up and let it finish cooling off. The bread tastes best when it has cooled to room temperature.
Once cooled off, store the zucchini bread at room temperature, wrapped in plastic.