Heat oven to 350°F. Lightly grease 8-inch square pan with shortening or cooking spray. In small bowl, toss chopped apple with lemon juice. Add brown sugar; stir well to coat. Set aside.
In medium bowl, stir pancake mix, granulated sugar and cinnamon with whisk; stir in milk, butter and vanilla. Fold apple mixture and any accumulated juices into batter. Spread in pan.
In 2-cup glass measuring cup, microwave apple juice on High 2 to 3 minutes or until boiling. Using a spoon, gently drizzle hot apple juice over batter (some batter may float once juice is added).
Bake 30 to 35 minutes or until cake layer forms on top and springs back when lightly touched. Cool 25 minutes. Serve cake warm with whipped cream and sprinkled with additional cinnamon.