Place shredded zucchini on paper towels for a few minutes to drain some but not all liquid. In one bowl, mix together the wet ingredients: shredded zucchini, eggs, oil, butter, vanilla extract, and brown sugar. In another bowl, mix together the flour, salt, cinnamon, cocoa powder, walnuts, baking powder, and baking soda. Gently fold the dry ingredients into the wet ones, stirring in ¾ cup chocolate chips.