In a large bowl whisk the eggs, and then stir in the pumpkin, maple syrup, vanilla, baking powder, pumpkin pie spice, cinnamon, and salt. Whisk in the milk. Then add the oats, mix to thoroughly incorporate, and pour the mixture into the prepared baking pan. (At this point, you may cover and refrigerate the oatmeal for several hours or overnight. In this case, much of the liquid will be absorbed by the oatmeal and it may cook a few minutes quicker, so check oven a little early.) Evenly distribute the banana slices over the top of the oatmeal.