Preheat oven to 350°. Butter an 8x8-inch baking dish or spray with non-stick cooking spray. Set aside.
In a mixing bowl, add chopped apples, granulated sugar, 3⁄4 teaspoon cinnamon, and lemon juice.
Stir to combine, then transfer to the prepared baking dish.
In a separate mixing bowl, add topping ingredients (brown sugar, oats, fl our, 1 teaspoon cinnamon, salt, and diced butter).
Use a pastry blender to cut the butter into the oat mixture, using a slight downward twisting motion, until the mixture resembles pea-sized crumbs. Or you can use two forks or your hands to cut butter into the mixture.
Spread topping over apples in baking dish and gently pat to even out.
Bake 40–50 minutes until golden brown and bubbly.
Serve warm.