Preheat oven to 350 degrees

Mix together all dry ingredients in a medium. In a large bowl, mix together wet ingredients until well combined and add the dry mixture. Mix until well-combined.  

In a greased 13x9 pan, press down half of the mixture. Spread out mixture until it entirely covers the bottom of the pan. Top with overlapping layers of apple slices. 

On a piece of wax or parchment paper, press down the other half of the oat mixture until it is the same size as the 13x9 pan. Lift up the wax/parchment paper and flip on top of the apples. Press down, especially the sides. Use extra flour on your hands if needed to prevent sticking.

Cook for 25 minutes. Let cool before slicing into 15 pieces. Store leftovers in the fridge.