01 - Preheat the oven to 350°F and grease an 8x8-inch baking dish.
02 - In a large bowl, toss the sliced apples with lemon juice, sugar, cinnamon, nutmeg, and flour until evenly coated. Spread mixture evenly in the prepared dish.
03 - In a separate bowl, mix oats, flour, brown sugar, cinnamon, and salt. Add cold, cubed butter and work it into the dry ingredients using fingers or a pastry cutter until coarse crumbs form.
04 - Evenly sprinkle the topping over the apple layer.
05 - Bake for 40 minutes until the topping is golden and apples are bubbly.
06 - Allow to cool slightly before serving. Serve warm, optionally with vanilla ice cream or whipped cream.