Preheat your oven to 350 degrees. Rub some sunflower oil on a paper towel and lightly grease a 4 x 9 inch loaf pan and set aside.
In a large bowl, add the sugars, oil, eggs, and milk to thoroughly combine.
In a separate bowl, sift together the flour, baking powder, soda, salt, and spices. Whisk together to evenly distribute. Add the dry ingredients to the wet mixture and stir till just combined. Carefully, fold in the zucchini and walnuts if using.
Pour the batter into the greased loaf pan using a flexible spatula to get all of it. Gently tap the pan on the counter to remove any air bubbles and if needed smooth any remaining lumps on the top.
Bake for approximately one hour in the lower third of your oven or until a toothpick inserted in the middle comes out clean. If the top starts to get too brown, lay a loose sheet of aluminum foil over it for the last bit of cooking time. When the bread is cooked, remove it from the oven and onto a cooling rack. Gently run a sharp knife around all four sides of the loaf pan. Let it cool for about 10 minutes and then invert it to cool completely out of the pan on the cooling rack.