@suzzlo yes, enable the Suunto plus app, begin the workout, stand still for 2 minutes, get a report with the HRV statistics.
I am not sure what is a widget, but all you need is to store the HRV measurements for a couple of minutes and then report that. Other tests (e.g., threshold) that are bundled as a Suunto plus app, do similar things, if I am not mistaken.