This works on Fedora and probably other distributions as well, though this uses HTTP which might be less optimal than FastCGI with Fos. I got Fos to compile with Mono but it's not usable yet, it can't find IAppBuilder in my "console" application no matter what references or using directives I add. Nowin compiles cleanly but the example projects don't, so it'll take some effort to get it to work. Things are progressing, though. But I really can't recommend anyone use Mono for web development as it stands.
you can work around that issue if you make an empty asp.net project and then use nuget to install-package nancy.hosting.aspnet
at least i think so, i haven't been doing .net in a while