- Combine green apple, rhubarb, onion, apple juice, dried cranberries, honey and ginger in a medium saucepan.
- Cover and cook over medium heat, stirring occasionally, until the rhubarb is soft and the apple is tender but not mushy, 10 to 12 minutes.
- Remove from the heat and let stand for 5 minutes. Stir in vinegar.
- Remove the ginger; serve the sauce warm, at room temperature or chilled.