Peel the zest from a Clementine as a large strip and keep aside. Juice all the clementines to make about half a cup of juice. Refrigerate the juice.
Heat the oil and saute the onions until they turn translucent. Add the pumpkin chunks and cook everything for a while. Add the vegetable broth.
Meanwhile in a cheese cloth, place the ginger, cinnamon stick and the clementine zest, and tie it tightly. Add to the cooking vegetables. Close the lid and cook the vegetables for few minutes until they turn soft.
Remove the cheesecloth and using a hand blender, puree the soup along with the clementine juice.