Preheat oven to 350°F. Line a 9×13-inch pan with parchment paper and spray with non-stick baking spray.

In a mixing bowl, beat together the butter, brown sugar, and granulated sugar until light and fluffy. Add flour and mix until combined. The dough will be crumbly.

Press dough evenly into the bottom of the prepared pan. Bake for 16 minutes. Remove from oven and let cool on a rack.

In a large bowl, combine apples and lemon juice and toss to coat. Add cinnamon, flour, sugar, and salt. Toss until apples are coated and arrange evenly on top of the crust.

In another bowl, combine oats, both sugars, cinnamon, and flour. Cut in the cubed butter until it resembles a coarse meal.

Sprinkle the topping evenly over the apples.

Bake for 45 to 50 minutes, or until the topping is golden brown and the apples are bubbling.

Remove from oven and cool on a rack for at least 1 hour before serving.