Pre-heat oven to 375°F.
In a large bowl, mix together flour, brown sugar, salt and 2 tablespoons granulated sugar.
Cut butter into flour, using a pastry blender or two knives, until mixture is the texture of coarse meal.
Add oats; use your hands to toss and squeeze mixture until large, moist clumps form; transfer to freezer to chill while apples are prepared.
In another large bowl, toss apples with lemon juice, cinnamon and remaining 1/2 cup granulated sugar.
Transfer to a shallow 2-quart baking dish and sprinkle with topping mixture.
Place baking dish on a rimmed baking sheet; place in the pre-heated oven and bake until golden and bubbling; 55 to 65 minutes.
Remove from the oven and allow to cool 10 minutes before serving.