Hey Simmy, I too suffer from the seconds and thirds syndrome!
I have started eating from a bread place (small) and I pile the veg and salad on FIRST, then I eat the meat and if there are any potato (my weakness!!)
. Then if I do go back for seconds, I do the salad thing first... and if I am STILL hungry I drink a glass of water and WALK AWAY!!!
Good luck with your habit changing!