Heat the oven to 375F. Lightly grease an 8-inch square baking dish.

Peel the apples if you like, then core and slice them about a quarter inch thick. Put them in a large bowl with the lemon juice.

Add 2 tablespoons of maple syrup, the cornstarch, 1.5 teaspoons of cinnamon, and the nutmeg. Toss until every slice is coated and no dry cornstarch remains. Spread the apples in the baking dish.

In the same bowl, stir together the oats, almond flour, pecans, the remaining 2 tablespoons of maple syrup, the half teaspoon of cinnamon, and the salt.

Melt the butter and pour it over the oat mixture. Stir with a fork until it clumps. Scatter the topping over the apples in an even layer.

Bake 40 to 45 minutes, until the topping is deep golden and the apple juices bubble at the edges. If the topping browns too fast, tent loosely with foil for the last 10 minutes.

Let it rest 15 minutes before serving so the filling thickens. Serve warm, on its own or with a spoonful of plain Greek yogurt.