I would do stuffed peppers for an extra main. You can fill them with any kind of meat you like fish/poultry/red then add some form of rice in.
Your mains where you've just said chicken or whatever would need some more description. Maybe say with a tomato sauce and stir fryed fresh veg?
A good idea might be to look up websites of resturaunts and see what sort of food theyre offering.
You've got a lot of salads for your starters how about doing some kind of bruschetta? Or a fish cake of some sort.
Tuna salad could be upgraded for a salad nicose which I dont thinks too bad for you? Anchovies, tuna, egg, tomato?