Heat oven to 350°F. Spray 13x9-inch pan with cooking spray. In large bowl, with electric mixer on medium speed, beat all filling ingredients until smooth. Pour into pan.
In medium bowl, mix crystallized ginger, cake mix, walnuts and butter until well blended. Sprinkle evenly over filling.
Bake 40 to 50 minutes or until top is golden brown. Cool at least 30 minutes before serving.
To serve, cut into squares; place on individual dessert plates. Top each serving with whipped cream. If desired, sprinkle with additional chopped crystallized ginger. Store in refrigerator.