Preheat oven to 325°F (165°C). Grease and flour two 8x4-inch loaf pans.
In a large bowl, whisk together flour, salt, baking soda, baking powder, and cinnamon.
In another bowl, beat the eggs, oil, sugar, and vanilla until well blended.
Stir the wet mixture into the dry ingredients until just combined.
Fold in the zucchini and walnuts, if using.
Pour the batter evenly into the prepared loaf pans.
Bake for 60–70 minutes, or until a toothpick inserted into the center comes out clean.
Let bread cool in pans for 20 minutes before removing to a wire rack to cool completely.