In large microwave-safe bowl, melt together the chocolate and oil. Stir until smooth. Add the grapes and stir until coated. Sift the powdered sugar over the grapes and stir until grapes begin to separate.

Pour the coated grapes onto a baking sheet that has been lined with a silicone baking mat or parchment paper.

Refrigerate for about 10 minutes. Remove the grapes from the sheet and store in an air-tight container in the refrigerator until ready to serve.