Stir yogurt if not premixed. Spoon into ice cube tray compartments. Freeze until completely frozen, 3 or 4 hours. Remove cubes from tray, place in bowl of electric food processor and process until finely chopped. Add strawberries and orange peel. Process just until almost smooth. Serve immediately or place in freezer and stir occasionally until firm enough to scoop, 1 to 2 hours. Makes 6.5-cup servings. Each serving: 90 calories, 3 grams protein, 18 grams carbohydrates, 1 gram fat, 41 milligrams sodium, 3 milligrams cholesterol.