The trick for a tender and juicy medallion is not to overcook it.  A nice technique is the tenderise, sear and bake method.

Tenderise: Tenderise the meat between cling film and flatten it with a rolling pin, or bottom of a pan before cooking.  It is important to achieve a thickness of 1cm to avoid over or undercooking it.

Sear: Fry on one side over a medium heat for 3 minutes.

Bake: Turn the medallions over and then oven bake for 6-8 minutes at 180°C, 160°C Fan, Gas Mark 4.

Rest: Allow the meat to rest for a couple of minutes after cooking and ensure juices run clear.

A quick 10 minute marinade with a pre-bought seasoning and vegetable oil can also help tenderise the meat before cooking.