For Cake: 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 mixing bowl using an electric mixer on medium speed for 2 minutes. Pour batter into pan. Bake 34 to 38 minutes or until toothpick inserted in the center comes out clean. Cool cake completely.
For Mousse Filling: BEAT softened cream cheese in large bowl with electric mixer on medium until soft. Blend in frosting and lemon juice. Fold in whipped topping.
TRIM edges from cake. Cut cake into 1-inch cubes. Place filling in decorator bag or reseable plastic bag. Cut off corner of plastic bag. Combine berries in a medium bowl. Layer in each of ten 8-ounce parfait glasses: 1/2 cup mixed berries, 9 cake cubes and 1/2 cup mousse filling. Begin layering with 1/4 of the berries, 3 cake cubes and 1/3 of the filling. Repeat 2 more times ending with berries. Garnish with straw, if desired. Chill until ready to serve.