Preheat the oven to 325°F and grease two 8x4 or 9x5-inch loaf pans.

In a large bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt.

In another large bowl, whisk together the sugar, vegetable oil, eggs, and vanilla. Add the grated zucchini and fold to combine.

Add the dry ingredients to the wet ingredients and mix until just combined. Fold in the walnuts.

Divide the batter between the prepared pans and sprinkle with walnuts. Bake for 40 to 55 minutes, or until a toothpick inserted comes out clean and the tops of the loaves spring back to the touch.