Heat oil in a large pot over medium-high heat. Add onion and cook, stirring often, until softened and translucent, about 4 minutes.
Stir in garlic, ginger, curry paste, and serrano; cook, stirring, for 1 minute.
Stir in sweet potatoes and water; bring to a boil. Reduce heat to medium-low and simmer, partially covered, until the sweet potatoes are soft, 10 to 12 minutes.
Transfer half of the soup to a blender, along with coconut milk and peanuts; puree. (Use caution when pureeing hot liquids.)
Return to the pot with the remaining soup. Stir in beans, salt, and pepper; heat through.
Remove from the heat. Stir in cilantro and lime juice. Serve with pumpkin seeds and lime wedges.
