Preheat your oven to 350F. Grease a large baking dish and set it aside.
In a deep pot or saucepan, melt the butter. Add the chopped chayote and water. Cover the pan and let it simmer for 7-8 minutes, until tender.
Once the chayote is tender, add the lemon juice, cinnamon, apple extract, xanthan gum, and both brown sugar substitutes. Mix well until combined. Continue to simmer for another 3 minutes.
Transfer the mixture into the greased baking dish. Bake in the oven for 8-10 minutes. While the filling is baking, prepare the crisp topping.
In a mixing bowl, combine the almond flour, chopped almonds, shredded coconut, sugar-free powdered sugar, and melted coconut oil. Mix until well combined.
Remove the baking dish from the oven and sprinkle the crisp topping evenly over the filling. Place it back in the oven and bake for an additional 10-15 minutes, until the top is golden brown.
Remove from the oven and let it sit for 10 minutes before serving.