Preheat the oven to 350°F and line a 9x13 baking dish with parchment paper.
In a stand mixer or with hand beaters, cream together the butter, sugar and brown sugar until light and fluffy.
Add the vanilla extract and eggs, one at a time, beating well after each egg.
Mix in the flour, cinnamon, baking powder and salt just until combined.
Add the rolled oats 1 cup on time mixing just until incorporated.
Firmly press a little over half of the dough into prepared baking dish. Set remaining dough aside.
In a mixing bowl, combine the chopped apples, lemon juice, sugar, cinnamon, salt and flour. Mix so all the apples are evenly coated.
Spread the apples in an even layer over the crust.
Place tablespoon pieces of flattened dough over the apples letting some filling peek through.
Bake for 60-65 minutes until the edges and top are golden brown.
Let cool completely before slicing and serving.