01 - Set oven temperature to 350°F (175°C).
02 - Combine sliced apples, granulated sugar, cinnamon, lemon juice, and flour in a large bowl; toss to evenly coat.
03 - Transfer the apple mixture into a greased 8x8-inch baking dish, spreading it evenly.
04 - In a separate bowl, blend granola, rolled oats, brown sugar, flour, cinnamon, and salt; stir in melted butter until crumbly and combined.
05 - Evenly sprinkle the granola mixture over the apple layer in the baking dish.
06 - Bake for 40 minutes until the topping is golden brown and apples are bubbling and tender.
07 - Allow to cool at least 10 minutes before serving; serve warm, optionally with vanilla ice cream or whipped cream.