I used to live on pasticcio when i was a student, it's essentially posh pasta bake
Off the top of my head I would do a SW version as follows.
Dry fry lamb mince (will have to syn that as no extra lean available in shops), drain off fat and add chopped onion, garlic, oregano, big squeeze of tomato puree, tin of chopped toms and 200ml veg stock. Add a pinch of cinnamon to the sauce and simmer for 20 mins.
Cook your pasta till it's firm, I used to use the cheapest penne pasta I could find as it worked well soaking up the flavours. For SW purposes then some good wholemeal pasta would probably be a lot more filling.
Whilst this is boiling mix up 1 pot of fat free yoghurt, 1 egg and 1 hexa of cheese. A pinch of mustard powder makes this sauce taste a bit more cheesy I think.
Chuck pasta into a casserole dish, cover with your lamb mixture and then top with your cheesy mix. Sprinkle on another hex of cheese and bake until golden brown and bubbling.
You could layer pasta, lamb, pasta, lamb and then topping if you wanted it to look a bit nicer when serving too
Serve with a greeky salad with lots of olives (8 for 1 syn)