Combine pumpkin and 1/3 of the chicken broth in a deep pan over medium-low heat. Simmer, covered, until pumpkin is soft, about 15 minutes.
Remove from heat and puree with an immersion blender. Add remaining chicken broth, sugar, salt, and pepper. Cook until flavors combine, about 5 minutes.
Ladle into bowls and serve with a dollop of Greek yogurt.
