Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish.
Mix Dry Ingredients: In a large bowl, whisk together flour, cinnamon, baking soda, salt, and baking powder.
Prepare Wet Ingredients: In a separate bowl, combine grated zucchini, sugar, oil, eggs, and vanilla extract. Mix well.
Combine Mixtures: Gradually add the dry ingredients to the wet mixture. Stir gently until just combined. Fold in chopped walnuts.
Bake the Cake: Pour the batter into the prepared baking dish. Bake for 45 minutes, or until a toothpick inserted into the center comes out clean.
Cool and Serve: Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack. Let it cool completely before slicing.