Preheat oven to 350 degrees. Spray a 9x9 baking pan lightly with cooking spray.
In a large bowl, whisk together the vegetable oil, sugar, eggs, and vanilla until smooth.
In a medium bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt. Add the flour mixture to the egg/sugar mixture. Mix until combined, do not overmix.
Wrap zucchini in a clean kitchen towel or paper towel and squeeze excess liquid. Fold shredded zucchini and crushed walnuts into the batter.
Pour batter into prepared pan and spread evenly. Bake until a tester comes out clean, about 40-50 minutes. Cool for about 30 minutes on a wire rack.
Store in airtight container at room temperature for up to three days.