In a medium bowl, mix the cocoa, white sugar, and vegetable oil together. Beat one egg at a time into the mix, then stir in the vanilla extract. In a separate bowl, combine the flour, baking powder, and salt. Stir the flour mixture into the cocoa mixture to make the dough. Cover that dough let it chill for at least 4 hours.
Turn the oven up to 350 F. Line a cookie sheet with parchment paper. Using a scoop, roll the dough into one inch balls. Coat each ball in the sugar, then place them on the prepped sheet. You're likely going to have a lot of dough, so you might need to prep an additional cookie sheet.
Bake your sheet(s) in the oven for 10 to 12 minutes. Let the cookies stand on the sheet for a minute, then transfer them to wire racks to cool.