Preheat oven to 425 degrees F.
Grate zucchini into a paper towel or dish cloth. Use the paper towel to squeeze the water out of the zucchini. Sprinkle with ¼ tsp of salt and let it sit for 10 minutes. Then squeeze out any excess water, squeeze as much water out as possible. You should have ½ cup of zucchini after it's been drained and squeezed.
Combine flour, baking soda, baking powder, salt, cinnamon, allspice, nutmeg, ginger, and cardamom in a large bowl and whisk together. Set aside.
In a separate bowl, combine brown sugar, sugar, vegetable oil, sour cream, and eggs. Whisk together until smooth then add vanilla extract, pumpkin puree, and grated zucchini and mix to combine.
Add the flour mixture to the wet ingredients and then fold in the chopped walnuts.
Cover the dough with plastic wrap or a kitchen towel and let it sit at room temperature for 15 minutes.
Add muffin liners to the muffin pan in every other muffin cup. Fill each lined muffin cup with batter. You can spread this out among two 12-cup muffin pans.
Bake at 425 degrees F for 5 minutes then reduce the temperature to 350 degrees F for 18 minutes, until a toothpick comes out clean. Allow muffins to cool on a wire rack.