Heat oil in a large saucepan or large pot over medium-high heat. Add onion and a pinch of salt, sauté 5 minutes until onion is soft. Stir in ginger, cook 1-2 min.
Puree soup using an immersion blender or in small batches using a regular blender or food processor. Return pureed soup to pot and stir in 1 cup light coconut milk and lime juice.