I'm not being facetious, but this might be a personal problem (not being able to get your mind off of work). For people who experience this, something like meditation might help, seriously. I certainly wouldn't fault an employer.
I'd love a 30 work week (if I wasn't trying to fast track towards retirement): those 10 hours (or more if working 4 days and not having to commute one weekday) would be entirely mine.