Preheat oven to 350 degrees. Place frozen fruit (do not thaw) evenly in the bottom of a 9 x 13" baking pan. In a medium sized bowl, lightly mix together the powdered cake mix and seltzer. Pour over the frozen fruit and bake uncovered on center rack for about 55-60 minutes or until golden brown. Serve warm. Goes great with a scoop of ice cream on top.