Preheat oven to 350 F degrees. Butter an 8x8 baking dish. You could use non-stick spray instead, but then you'll have to sort out your life's priorities. Set aside.
In a mixing bowl, add chopped apples, granulated sugar, 3/4 tsp of the cinnamon and lemon juice. Stir to combine, then transfer to prepared baking dish.
In a separate mixing bowl, add topping ingredients (brown sugar, oats, flour, 1 tsp cinnamon, salt, and diced cold butter). Use a pastry cutter to cut the butter into the oat mixture, using a slight downward twisting motion, until mixture resembled pea-sized crumbs. Alternatively, you can use two forks or even your hands to cut butter into the mixture.
Spread topping over apples in baking dish, and gently pat to even it out. Make sure butter nodules are evenly dispersed if they fall to the edges. Bake 50-60 minutes, until golden brown and bubbly.