Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a 9x13-inch baking dish.
Combine flour, cinnamon, baking soda, salt, and baking powder in a bowl.
Mix zucchini, sugar, vegetable oil, eggs, and vanilla in a separate bowl.
Add flour mixture to zucchini mixture and stir until just combined.
Stir in walnuts, then pour batter into the prepared pan.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 45 minutes.
