Preheat the oven to 350 degrees F. Lightly mist an 8 x 8 baking pan with nonstick vegetable oil spray.
Place the diced apples in a microwave-safe container and microwave for 2 minutes. Cool.
In a small mixing bowl, combine 1/4 teaspoon apple pie spice and 1 tablespoon sugar substitute and reserve.
Combine the flours, salt, baking soda, baking powder, and 1 teaspoon apple pie spice in a mixing bowl. Set aside.
In a mixing bowl, whisk together the oil and 1 cup sugar substitute for 1 minute. Add the egg substitute and vanilla and continue to whisk for 1 minute. Add one-third of the dry ingredients and mix to combine. Add one-third of the Glucerna Shake and mix to combine.
Repeat the process two more times. Scrape the inside surface of the bowl and fold in the steamed diced apples. Pour the batter into the prepared pan. Arrange the sliced apples on top of the cake batter and sprinkle with the reserved spice and sugar substitute blend.
Bake for 35 to 40 minutes or until a toothpick inserted into the center of the cake comes out clean. Transfer to a wire rack and cool. Slice and serve.