Preheat oven to 350 F degrees and butter an 8x8 baking dish or spray with non-stick cooking spray.
In a mixing bowl, combine peeled and chopped apples, granulated sugar, 3/4 tsp ground cinnamon, and lemon juice. Stir to combine.
Transfer the spiced apple mixture to the prepared baking dish.
In a separate bowl, mix brown sugar, oats, flour, 1 tsp ground cinnamon, and a pinch of kosher salt.
Cut cold diced butter into the oat mixture using a pastry cutter, two forks, or hands until pea-sized crumbs form.
Spread the crumb topping evenly over the apples in the baking dish and gently pat down.
Bake for 40-50 minutes until the topping is golden brown and the apple mixture is bubbly.
Serve warm, optionally topped with vanilla ice cream or whipped cream for extra indulgence.