1. Heat butter in a large heavy saucepan over medium heat 1 minute. Add green onions and orange zest, and sauté, stirring occasionally, 5 minutes or until lightly browned. Add peas, reduce heat to medium-low, cover, and cook 10 to 15 minutes more or until soft, stirring once or twice. If peas threaten to scorch, add a small amount of vegetable broth, and stir.
2. Scoop into a blender or food processor, add 1 cup broth and next 4 ingredients, and puree until smooth. Transfer half of mixture to a large nonreactive pitcher.
3. Add remaining 2 cups broth to pea mixture in blender, and puree at high speed until smooth. Combine with mixture in pitcher, cover, and chill at least 2 hours before serving.
4. Whisk well or homogenize with a blender, and ladle into chilled soup bowls. Garnish, if desired.