What do you eat for dinner? Could you bring a smaller portion of that for lunch?
That is what I do.
Another thing I do is make grain/bean salads. You can serve them on a bed of lettuce and they are really good and filling. You could also have a side of chopped veggies (like carrots, celery, cucumbers, etc) to boost your veggie count.
Here is one of my favorite recipes: (I reduce the amount of oil)
http://www.katu.com/amnw/recipes/41748467.html