Heat oven to 350°F. Spray 15x10x1-inch baking pan with nonstick cooking spray. Prepare cake mix as directed on package using water, oil and eggs. Pour batter into sprayed pan.
Bake at 350°F. for 25 to 30 minutes or until toothpick inserted in center comes out clean. Cool in pan on wire rack for 30 minutes or until completely cooled.
Spread frosting over cooled cake. Scatter candies over frosting.