The SW website says:
Moussaka, Vegetable, average portion (550g serving) 20 syns
Out of the options under the Vegetarian list, I would say that the Couscous B'Khodar or Mahashi wouldn't be too bad maybe? Most of the ingredients listed for those are free, so you'd just need to count syns for any oil used (6 syns per tbsp.) but otherwise they might be ok.