In a large stock pot over medium-high heat, add oil, onion, garlic and sweet potatoes. Let cook for 5 minutes, stirring occasionally, to get tender.
Add in lemongrass, ginger, broth, coconut milk and curry paste. Stir to combine. Reduce heat to medium and cover with lid. Let cook for 45 minutes.
Using an immersion blender, blitz soup until potatoes are pureed. Add lemon zest and juice, potstickers and spinach. Recover with lid and cook for 10 minutes more.
Serve in a shallow bowl with 5-6 potstickers and sprinkle of cilantro.