HEAT oven to 350°F. Coat 13 x 9-inch baking pan with no-stick cooking spray. Combine cake mix, water, oil and eggs in large bowl with electric mixer until moistened. Beat on medium speed for 2 minutes. Spread 2 cups batter evenly in prepared pan.
BEAT cream cheese, brown sugar and water in small bowl with electric mixer until creamy. Add filling mix and peppermint extract. Beat until smooth. Layer evenly on top of batter to within 1/2-inch of edge. Spread remaining batter on top.
BAKE 25 to 28 minutes or until toothpick inserted in center comes out clean. Cool completely. Spread with frosting. Sprinkle with chopped candy.