Preheat oven to 375 degrees F. Line rimless baking sheets with parchment paper. (Optional: toast the walnuts in the oven as it preheats, checking every 2 minutes or two, until they turn a shade darker and smell fragrant - about 8-10 minutes.)
In a large bowl, combine flour, baking powder, baking soda, salt and cinnamon. In a separate bowl, whisk together brown sugar, oil, zucchini, egg and vanilla extract. Add to dry ingredients, stirring until mostly combined with just a few floury streaks, then fold in chocolate chips and walnuts.
Drop batter by heaping tablespoonfuls onto prepared baking sheets, spacing 1 inch apart. Bake about 10 minutes, until slightly springy to the touch. Cool 2 minutes on baking sheets before transferring to wire racks to cool completely.