Preheat oven to 375 degrees Line rimless baking sheets with parchment paper. (Optional: toast the nuts 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 spices. In a separate bowl, whisk together the pumpkin, brown sugar, oil, egg and vanilla extract. Use a rubber spatula to scrape this mixture into the dry ingredients, gently folding until mostly combined. When just a few floury streaks remain, fold in the nuts and raisins (if using).
Drop batter by heaping tablespoonfuls (so actually about 2 tablespoons per cookies) onto prepared baking sheets, spacing 1 inch apart. Bake 8-10 minutes, until slightly springy to the touch (a light press with your finger won't leave a strong indent). Cool 2 minutes on baking sheets before transferring to wire racks to cool completely.