Cut Butter Into Dry Ingredients: Whisk almond flour, xanthan gum, coconut flour, and erythritol together in a mixing bowl until well combined. Add cold butter and rub it into the dry ingredients until it resembles bread crumbs.
Add Remaining Ingredients: Add the lemon zest, apple cider vinegar, and egg to the crust ingredients, and mix to form a dough. Flatten the pastry dough into a disk shape, cover it with plastic wrap, and chill dough in the fridge for 30 minutes.
Sweeten the Squash: Add the brown sugar substitute, cinnamon, nutmeg, allspice, cardamom, and lemon juice. Stir through and cook on low heat, stirring occasionally for 10 minutes, or until zucchini is fork tender.