Preheat the oven. Set your oven to 350°F (175°C). Lightly grease an 8x8-inch baking dish.

Prep the “apple” base. Peel chayote or zucchini. Halve and scoop out any seeds. Slice into thin half-moons, about 1/4-inch thick, until you have roughly 4 cups.

Soften the squash. In a large skillet over medium heat, melt 1 tablespoon butter. Add the sliced chayote/zucchini, 1/4 cup sweetener, 1 teaspoon cinnamon, apple pie spice (if using), lemon juice, and a pinch of salt. Cook 6–8 minutes, stirring often, until the slices begin to soften but still hold shape.

Add flavor and thicken. Stir in vanilla and apple extract. If you want a saucier filling, sprinkle on xanthan gum or glucomannan and stir for 30–60 seconds until slightly thickened. Remove from heat and spread the mixture evenly in the prepared baking dish.

Make the crisp topping. In a bowl, combine almond flour, chopped pecans, remaining sweetener (start with 1/4 cup; adjust to taste), 1 teaspoon cinnamon, and a pinch of salt. Melt the remaining 5 tablespoons butter and stir it into the mixture until crumbly and evenly moistened.

Top and bake. Sprinkle the crumble over the filling, covering it in an even layer. Bake for 25–30 minutes, until the topping is golden and the filling is bubbling at the edges.

Rest and serve. Let it sit for 10–15 minutes to set. Serve warm with sugar-free whipped cream or a scoop of keto ice cream.