Preheat your oven to 325°F and grease two 8x4-inch loaf pans.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.
In another bowl, beat the eggs, then mix in the oil, sugar, and vanilla until well combined.
Stir in the grated zucchini.
Gradually add the dry ingredients to the wet mixture, stirring just until blended.
Fold in the nuts if you’re using them.
Pour the batter evenly into the prepared pans.
Bake for 60–70 minutes, or until a toothpick inserted in the center comes out clean.
Cool in the pans for 10 minutes, then remove to a wire rack to cool completely.