Preheat oven to 375 degrees. 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, and use your hands to toss and squeeze mixture until large, moist clumps form. Transfer to freezer to chill while you prepare apples.
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, and bake until golden and bubbling, 55 to 65 minutes. Let cool 10 minutes before serving.