Are you working in an office or from home? What sort of clothes will you be wearing? How much private space will you have? Is there anywhere nice to go for a walk? Are you sitting most of the day? If you are, then I think I would go for a 20/30 minute walk with an audiobook, do 10 minutes of yoga if you have the space, and then eat in the last 20/30 minutes.
I wouldn't eat at my desk outside my lunch hour at a new job: if other people do then maybe, but you want to make a good first impression and eating at your desk when you get a paid hour for lunch seems a tad cheeky (though I haven't worked anywhere with paid breaks or a full hour for lunch before, so maybe it's quite common).
If you're working from home and no one will know that you're scoffing a sandwich then I would go for a lunch swim a few times a week.