Place chocolate in microwave safe bowl. Heat for 30 seconds, stir and continue heating for 10 seconds at a time, stirring after each heating until completely melted. Set a side to cool.
In a large bowl, mix together oil, sugar and melted chocolate. Add eggs one at a time, mixing well after each addition. Add vanilla and beat well.
In a medium bowl, whisk together flour, baking powder and salt. Gradually add dry mixture to wet mixture until well combined.
Cover bowl with plastic wrap. Place in refrigerator to chill several hours or overnight.
Remove from refrigerator and set on counter for about 20 minutes to warm up slightly.
Preheat oven to 350 degrees. Line baking sheets with parchment paper or silicone mat.
Place powdered sugar in medium bowl. Roll dough into balls and coat with powdered sugar.
Bake for 10-12 minutes or until edges are set.
Remove from oven and let set on baking sheets for 2-3 minutes.
Transfer to wire cooling rack and cool completely. Store in airtight container for up to 5 days.