I have not attempted the following tutorial from a Solidworks Surfacing guru but thought someone might do something similar with FreeCAD. My experience is to limited with FreeCAD and therefore inefficient or inelegant so i will not attempt it. The link is to a picture of modern sunglasses but not the actual tutorial. The claim is that it will stretch your surfacing abilities.
https://dezignstuff.com/new-page-added- ... unglasses/