In a large bowl, whisk together the oil, sugar, and cocoa. Add the eggs, one at a time, and whisk well after each addition. Add the vanilla and whisk again. Add the flour, baking powder, and salt and mix well with a wooden spoon or silicone spatula. Place the dough in the refrigerator for 1 hour.
Line three baking sheets with parchment, or bake in batches. Use a tablespoon to scoop up the dough and roll into balls about 1 inch in diameter. If you’d like to coat the cookies in confectioners’ sugar, place the confectioners’ sugar in a small bowl. Roll the cookie balls in the confectioners’ sugar until they are heavily coated with sugar. Place the cookie dough balls on the prepared baking sheets about 1½ inches apart. Place the sheets in the freezer for at least 15 minutes.
Preheat the oven to 350ºF. Bake for 12 to 16 minutes, depending on how chewy or crunchy you like your cookies. The cookies will spread and crack on top when they are almost done. Slice the parchment onto cooling racks and let cool.