Combine flour, baking powder, salt, and cocoa powder well. In a separate bowl, blend together sugar, oil, eggs, and vanilla. Add flour mixture to wet ingredients and blend until well combined. Refrigerate dough overnight.
Working in batches (keep remaining dough in fridge):
Cover a Goodcook Mega Cookie Sheet with parchment paper, and preheat oven to 350 degrees. Place powdered sugar in a bowl, and roll into balls of about 1 inch. Roll in powdered sugar, making sure to coat well. Bake 12-14 minutes.