For a 2 kg gammon joint
Put the gammon on the bottom rack and cover loosely with foil. If you have a Halogen Oven smaller than 12 Litre, use the extension ring to take the heat source higher.
Cook at 160C for 1 hour, turn and cook for another 1 hour. Remove the foil and let it brown for 10 minutes, still at 160C, then turn it for another 10 minutes to brown all round.
Gammon will vary in thickness and shape so to ensure thorough cooking times may vary a bit. Test with a skewer to make sure juices run clear