Heat oven to 350°F. Spray 15x10x1-inch baking pan with nonstick cooking spray. In large bowl, combine all bar ingredients; stir 50 to 75 strokes until dry mix is moistened. Spread batter evenly in greased pan.
Bake at 350°F. for 25 to 35 minutes or until toothpick inserted in center comes out clean. Cool 45 minutes or until completely cooled.
In small bowl, combine all frosting ingredients; beat until smooth. Spread over cooled bars. Decorate as desired. Store in refrigerator.