In a dutch oven (or heavy large pot), heat oil over med heat. Add onions and saute until just translucent.
Peel and chop sweet potatoes and add to onion. Stir.
Add ginger, cinnamon. Stir.
Add in water and coconut milk and continue to cook over med heat until potatoes are tender.
Remove from heat.
Using a food processor, in batches, puree the potato mixture until smooth. Or, if you prefer, use an immersion blender.
Add pureed soup back to pot and continue to cook for approx. 15 minutes or until desired thickness.
Season with salt and pepper.
Serve hot. Top with a dash of cinnamon.