Preheat the oven to 350°F. Grease an 8-inch square baking dish.
In a large bowl, mix the sliced apples, lemon juice, granulated sugar, and 1 teaspoon cinnamon until evenly coated. Transfer to the prepared baking dish.
In a separate bowl, combine flour, oats, brown sugar, remaining 1 teaspoon cinnamon, and salt. Add cold butter cubes. Use a pastry cutter or your fingers to blend the mixture until it resembles coarse crumbs.
Sprinkle the crumb topping evenly over the apples. Bake in the preheated oven for 45 minutes, or until the topping is golden brown and the apples are bubbly. Check the tenderness of the apples before removing from oven.
Allow to cool slightly before serving. Serve warm, optionally with a scoop of vanilla ice cream.