Preheat oven to 375 degrees. In a large bowl, mix together flour, brown sugar, salt, and 2 tablespoons granulated sugar. Cut butter into mixture, using a pastry blender or two knives, until it is the texture of coarse meal. Add oats, and use your hands to incorporate into the rest of the topping mixture..Transfer to fridge to chill while you prepare apples.

In a large bowl, toss apples with lemon juice, cinnamon, and remaining 1/2 cup granulated sugar. Transfer to a shallow 2-quart baking dish, and with top with refrigerated oat mixture.. Place baking dish on a rimmed baking sheet, and bake until golden and bubbling, 55 to 65 minutes. Serve with a scoop of ice cream.