Peel, core, and slice the chayote squash into thin pieces.
Toss with lemon juice and microwave for 5–6 minutes until fork-tender.
In a skillet, melt butter and add chayote along with erythritol, cinnamon, nutmeg, and allspice. Cook for 8–10 minutes.
Remove from heat, stir in vanilla extract, and let cool.
Preheat oven to 375°F (190°C).
Roll out almond flour pie crust and place in a 9-inch pie dish. Add the cooled filling.
Cover with top crust. Crimp edges and cut slits on top for steam to escape.
Brush with egg wash.
Bake for 30–35 minutes or until golden brown.
Cool for at least 30 minutes before slicing. Serve warm or chilled.