Preheat the oven to 325 degrees and generously grease two 9 x 5 x 3-inch loaf pans or four mini-loaf pans.
Sift (or whisk) the flour, salt, baking soda, baking powder, and cinnamon into a large bowl. Stir in the nuts, if using. Set aside.
Mix the sugar, eggs, oil, vanilla, and zucchini in a large bowl. Stir in the dry ingredients with a wooden spoon.
Scrape the batter evenly into the prepared pans and bake the large loaves about 1 hour and 15 minutes, the mini-loaves 25 to 30 minutes, until a toothpick inserted in the center comes out clean, but not dry. Do not over-bake; the breads should be moist.
Variation: Sprinkle cinnamon and sugar on greased pans