Preheat oven to 350°F (175°C). Grease two 8x4 inch loaf pans or one 9x5 inch pan and set aside.

Grate the zucchini and place in a clean kitchen towel. Squeeze out as much moisture as possible. Measure 2 cups after squeezing.

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

In a separate bowl, whisk together eggs, oil, and vanilla. Stir in the grated zucchini.

Pour the wet ingredients into the dry ingredients and fold gently until just combined. Fold in walnuts if using. Do not overmix.

Divide batter evenly between prepared pans. Optionally sprinkle the tops with cinnamon sugar.

Bake for 50-60 minutes until a toothpick inserted in the center comes out clean. Tent with foil at 40 minutes if tops are browning too quickly.

Cool in pans for 10 minutes, then turn out onto a wire rack to cool completely. Slice and serve.