In a large bowl, whisk together almond flour, pecans, erythritol, stevia, cinnamon and salt. Next add in the butter chunks, stevia, and vanilla.
Use a pastry cutter or two knives to blend in until the mixture resembles coarse crumbs. Set aside.
The "Apple" Base
Preheat oven to 400F. In a small bowl, combine water and xanthan gum, whisking until combined.
In a separate large bowl, combine jicama, erythritol, stevia, lemon juice, cinnamon, and nutmeg, tossing to coat. Add water/xanthan mixture and stir well.
Spread mixture in a 10-inch cast iron skillet or 8x8 casserole dish. Sprinkle the crumble mixture evenly on top. Cover tightly with foil and bake 25 to 30 minutes.
Remove foil and cook an additional 5-10 minutes, or until mixture is bubbling and crumble is browned.