Place all ingredients, except the orange slices, in a blender and puree until smooth and creamy. Pour into glasses or tumblers. Slit the orange slices half way to the center. Garnish each glass with a slice of orange on the rim.
Per serving - 228 calories, 5 g fat (20% calories from fat), 12 g protein, 36 g carbohydrate, 2 g fiber, 0 mg cholesterol, 106 mg sodium