Hmm. I used to do some volunteer work for a children's summer camp run by my local Christian organisation and for a couple of summers I worked in the kitchens preparing meals for about 130 children and other leaders. In terms of mass catering, we certainly used to do things like Lasagne and spaghetti because they are pretty easy to prepare and then cook so I can see why your friends have chosen to make meals like that. :lol:
One year I made simple chicken fajitas for everyone. They were really easy as you can just bake some chicken and strips of vegetables and then add some seasoning or sauce to them. Heat the tortillas and people can make their own from a big communal pan of food, serve with sour cream, cheese, salad and maybe some rice or something.
With 11 people I would probably think of something like 'toad in the hole', but I'm not sure where you are from so that might just sound ridiculously weird. If you don't know what it is, then it's basically sausages in yorkshire pudding batter, which is baked and served with gravy and vegetables. It's actually really easy to make.