Preheat the oven to 350°F (175°C).
Combine the coconut sugar and almond flour in a medium bowl.
Stir in the rolled oats and chopped nuts.
Work in the solid coconut oil until the topping is evenly crumbly. Set aside.
In a large bowl, combine the sliced apples, maple syrup, lemon juice, arrowroot or cornstarch, cinnamon, nutmeg, and salt.
Toss until the apples are evenly coated.
Spread the apples evenly in the baking dish.
Scatter the oat topping evenly over the apples.
Bake for 40–50 minutes, until the filling is bubbling and the topping is golden and crisp.
Rest for 10–15 minutes before serving.