Preheat oven to 350 °F. Line a 9x13 cake pan with parchment paper.
In a medium bowl- combine all-purpose flour, baking soda, baking powder, salt, & spices. Whisk to combine and set aside.
Wash, peel and seed zucchini. Using a food processor- grate zucchini. Using a cheesecloth or paper towel, squeeze grated zucchini to release some of the moisture. Set aside
In a bowl of a stand mixer fitted with a paddle attachment- combine oil and sugars and mix on medium speed for 2-3 minutes or until combined.
Add eggs to the stand mixer, one at a time, mixing thoroughly before adding each additional egg.
Starting and ending with the dry ingredients, alternate mixing dry ingredients and buttermilk. Add 1/3 dry ingredients, mix on medium speed until combined. With the mixer on low, slowly stream in 1/2 the buttermilk. Continue by alternating the dry and wet ingredients, making sure to end with the dry ingredients.
Fold in the shredded zucchini and walnuts using a spatula- do not overmix!
Pour batter into the prepared baking pan and bake for 30-45 minutes or until a toothpick inserted into the center comes out clean.
Allow to cool on a cooling rack for 30 minutes until removing cake from the baking pan.