Combine first 3 ingredients in a large Dutch oven, and bring to a boil. Cover, reduce heat, and simmer 10 minutes. Combine 1 cup pumpkin mixture and peanut butter in a blender or food processor; process until smooth. Return mixture to pan. Stir in vinegar and next 5 ingredients (vinegar through garlic); cook 3 minutes or until thoroughly heated. Ladle into soup bowls. Sprinkle with cilantro, if desired.