Preheat the oven to 375 degrees F. Grease a 9" square baking pan and set aside.
Cut the apples into thin slices, and line the bottom of the baking pan with half of the slices.
In a large bowl, combine the oats, shredded parsnips, cinnamon, baking powder, and salt. Mix well and transfer this mixture to the baking pan, spreading it evenly with your hands on top of the apples.
In another large bowl (or the same one if you want), combine the milk, maple syrup, beaten egg, vanilla, and melted butter. Pour this over the dry mixture in the baking pan. Shake the pan slightly to let the liquid mixture seep through the oats and spread out.
Arrange the rest of the apple slices on top. Bake for 45 minutes, or until the top layer is golden brown and the apples are tender. Serve warm and enjoy!