Thaw one sheet of puff pastry until pliable to open without cracking but still cool to the touch.
Preheat oven to 375 degrees. Roll out into a 8" x 14" rectangle. Transfer to a parchment lined baking sheet.
Score edges of puff pastry creating a ½ inch border all around the pastry. You don't want to cut all the way through. Just make a score.
Peel and slice apples. Toss with lemon juice.
Mix cinnamon, apple pie spice, a dash of salt, and brown sugar. Add to apples and toss together. Let sit for a few minutes to draw out some juices.
Arrange apples as desired over puff pastry making sure to keep them inside scored border. Pour any remaining brown sugar mixture over apples.
Bake at 30-35 minutes or until apples are tender and pastry is golden brown.
Warm vanilla frosting in microwave until it reaches drizzling consistency. Drizzle over tart.Serve warm or at room temperature.