The caveat here is, how long is your lunch break? Let’s assume it's a traditional one hour. There is an awful lot you can achieve in one hour. If you’re trying to maximise that time, get the best bang for your buck so to speak, I would advocate interval-type training.
Say a minute on of running and jumping at 90 per cent of your maximum ability, followed by a minute of much gentler exercise – or even rest. You should start at a pace you can manage, and build the intensity up over time. You can do that sort of session with a warm up and a cool down in about thirty minutes, which leave you another 30 minutes to get changed, have a shower, have something to eat and get back to your desk.
We know from research we have done – and from the huge amounts of research done globally – that this form of interval training and exercise regime will give you benefits equivalent to much more prolonged bouts of aerobic style exercises.