Preheat your oven to 325°F and grease two loaf pans (8x4 or 9x5-inch).
In a large bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt until evenly combined.
In another large bowl, whisk together the sugar, vegetable oil, eggs, and vanilla until smooth.
Add the grated zucchini to the wet mixture and gently fold it in until combined.
Add the dry ingredients to the wet ingredients and mix gently until just combined. Do not overmix. Fold in the chopped walnuts.
Divide the batter evenly between the prepared pans and sprinkle extra walnuts on top.
Bake for 40 to 55 minutes, until a toothpick inserted into the center comes out clean and the tops spring back lightly when touched.
Let the bread cool before slicing and serving.