Lightly coat a large saucepan with cooking oil or nonstick cooking spray. Add onion, garlic, and carrots. Cook and stir over medium heat for 3 to 5 minutes or till onion is tender. Add peas, chicken stock or broth, and orange peel. Bring to boiling; reduce heat and cook, covered, over medium-low heat tillcarrots and peas are very tender, about 45 minutes. Cool slightly.
Place carrot mixture, half at a time, into a blender container or food processor bowl. Cover and blend or process till smooth. Return puree to saucepan.
Stir in orange juice, brown sugar, nutmeg, and ground red pepper. Cook and stir over low heat about 5 minutes or just till sugar has dissolved and flavors blend. Remove from heat and cool slightly. Pour soup into a medium bowl; cover and refrigerate 4 hours or till chilled.
To serve, add salt, brown sugar, or ground red pepper to taste, if desired. Stir sour cream until smooth, adding 2 tablespoons fat-free milk, if necessary; gently swirl it into soup. Sprinkle with chives. Serve cold.