Heat oil in a soup pot over medium heat. Cook onion for 6 to 7 minutes until softened, then stir in ginger and curry paste for 1 minute.
Add pumpkin, broth, coconut milk, soy sauce and brown sugar. Stir well and bring to a gentle simmer.
Cover partly and cook for 22 to 25 minutes, stirring occasionally, until pumpkin collapses when pressed with a spoon.
Remove from the heat and puree with an immersion blender until smooth. Stir in lime juice, then warm gently for 1 to 2 minutes if needed and divide among 6 bowls.