Lightly grease a 9x13 inch baking dish. Place the sliced apples in a large bowl and toss with the lemon juice; set aside.
In a medium bowl combine the flour, granulated sugar, cinnamon, and nutmeg. Sprinkle this mixture over the apples and toss well to coat. Pour mixture into prepared baking dish and set aside while you make the crumb topping.
For the Crumb Topping:
In a large bowl combine the flour, brown sugar, oats, pecans, baking powder, nutmeg and cinnamon.
Using a pastry blender or two forks, cut in the cold butter until the mixture resembles a coarse meal.
Sprinkle over apple mixture.
Bake in preheated oven for 45 to 50 minutes, or until the crumb is golden and the apples are tender.
Drizzle with salted caramel sauce and serve warm, with flaky sea salt and ice cream, if desired.