OK. I understand that "chocolate" is not a restaurant. But, if you go to Lausanne, you must eat chocolate.

There are literally hundreds of chocolate shops in Lausanne.

My personal favorite (because of proximity to where I lived) is Noz Chocolatier.   Located on a little side street (Rue Marterey) not far from the Bessieres metro stop.

Address: Rue Marterey 11, 1005 Lausanne, Switzerland

Website: http://www.noz-chocolatier.ch/