Combine the walnuts and pomegranate juice in the container of a blender or food processor. Process into liquid. (This can be done in small batches if necessary.) Add walnut-pomegranate mixture to the simmering chicken. Season with cardamom, cinnamon, saffron powder, and salt. Stir in the cubed squash. Transfer the entire mixture to a 9×13-inch baking dish.