"Experience working in a supervisory capacity'"
-which I don't have- "I undertook a period of secondment 15 years ago, where I supervised a member of staff for 6 months or so,"
Imposter syndrome.
Yes, I have supervised a member of staff. This included my finalising tasks after review. I set deadlines to staff assigned to me and checked periodically whether they were on target. I factored this into my working day.
I set reporting and catch up deadlines for the staff who I was supervising.....
I managed the workflow and training requirements of those under my supervision by identifying and addressing training needs.
My supervision role helped hone my productivity skills as I worked out how to prevent downtime by setting appropriate work deadlines, which brought the companies' holistic productivity up by X, Y, Z (something tangible)
I implemented a system which meant deadlines were met more easily (detail it)
Supervising others improved my ability to give feedback and so develop a more holistic view of projects.
-just off top of my head-
It's about selling yourself with tangible examples.