Preheat oven to 350°F.
Make the topping by mixing together sugar, rolled oats, almond flour and nuts. Add butter or coconut oil and combine until topping is crumb-like. Set aside.
Add apple slices to a large bowl with maple syrup, lemon juice, arrowroot powder, cinnamon, nutmeg and salt. Gently toss until all apple slices are coated.
Transfer apple mixture to greased 8x8 square baking dish or a 9-inch round pie pan.
Sprinkle crisp topping over apple mixture.
Bake for 45-50 minutes or until the apple filling is bubbly and the top is golden. Check the crisp around 30 minutes in. If the crisp seems to be browning too quickly, cover with foil for the remaining 15-20 minutes.
Cool on a wire rack for 5-10 minutes.
Serve warm with ice cream or whipped topping.
Store in an airtight container. Leftovers will store well at room temperature for 2-3 days or in the refrigerator for up to 5 days.