Mix the cocoa, sugar, and vegetable oil together in a large bowl.
Beat in the eggs one at a time, then add the vanilla.
Stir in the flour, baking powder, and salt.
Cover with plastic wrap and chill for at least 4 hours.
Preheat oven to 350 degrees. Line cookie sheets with parchment paper, set aside.
Scoop the dough and roll into 1-inch balls and roll in your hands until round.
Roll each cookie ball in powdered sugar and place on the baking sheets.
Bake for 10 to 12 minutes, until set but still soft. Remove from oven and allow to sit for one minute on the baking sheet before pressing a peppermint candy into the center of each cookie.