I would say to go with Harvester, the have unlimited salad and unlimited soft drinks (ie diet pepsi) which you go and refill yourself as and when you want it. Their menus have calories on them as well if you've saved up enough syns for dessert.
They do grilled chicken, steak, prawns. You get a free sauce with any grill as well, and they have the calories by them as well. Most sauces are under 80cals for the whole pot, quite a few under 40 (ie 2syns)
You can choose to have new potatoes without butter, jacket pot or rice to go with any grill as well.
..... I went there tonight haha.
I love Beefeater but they do bottomless chips with their meals... And i know i wouldn't be able to resist that.
Hope this helps.