Preheat oven to 350°F. Grease bottom and sides of 8x8x2-inch pan.
In medium bowl, whisk full pouch lemon filling, whipping cream and eggs together until eggs are well incorporated. Set aside.
Stir graham cracker crumbs, crust mix, and melted butter in a bowl until well blended. Press evenly into bottom of pan. Bake 12 minutes.
Whisk filling mixture again and then stir in mandarin oranges. Pour filling over hot crust. Bake 32-36 minutes or until center does not jiggle when shaken and top begins to brown. Cool completely and cut into squares. Sprinkle with powdered sugar, if desired. Store covered in the refrigerator.