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 - 259 calories, 6 g fat (18% calories from fat), 12 g protein, 44 g carbohydrate, 5 g fiber, 0 mg cholesterol, 113 mg sodium