Place first 4 ingredients in a blender; process until smooth. Place the blender container in freezer; freeze 1 hour or until slightly frozen. Loosen frozen mixture from sides of blender container; add yogurt. Process until smooth, and garnish with sliced banana, if desired. Serve immediately.
Note: For a chocolate-flavored shake, use reduced-fat chocolate milk instead of the plain fat-free milk, and reduce the sugar to 1 tablespoon.