Combine. In a large bowl (or a stand mixer), combine oil, cocoa powder, and sugar. Stir until well-combined. (It'll look like very dark wet sand). Add eggs 1 at a time, mixing in-between each addition to incorporate well. Add vanilla and stir to combine. Add salt, baking powder, and gluten free flour. Stir until just combined.
Chill the dough 3-4 hours (or overnight). Do NOT skip this step, or your cookies will spread too much in the oven.
Preheat & Prep. When ready to bake, preheat oven to 350 degrees F. Line a baking sheet with parchment and place powdered sugar in a bowl.
Scoop & Roll Cookie Dough. Use a scoop or a tablespoon to roll out 1" balls of chilled dough. Roll each cookie dough ball in powdered sugar to coat well.
Bake Cookies. Place 8-12 coated cookie dough balls on the prepared baking sheet. Bake at 350 degrees F. for 8-10 minutes, or until just the edges are set and the centers are still wet.
Cool. Allow the cookies to cool 2-3 minutes on the baking sheet to allow them to continue to set, then transfer to a cooling rack.
Repeat with remaining dough until all the cookies are baked.
Serve & Store. Enjoy cookies right away, or store in an airtight container at room temperature 2-3 days. Or, freeze 2-3 months.