My boyfriend ate no breakfast and usually crappy lunch everyday. For him its more of a time issue. He works 12 hours a day 5 days a week. So he doesn't have a lot of time to think about lunch and stuff. He was all for me making him lunches. He just eats whatever I put in it (of course I only put in food he likes). So I make sure to have something from every food group in his lunches. With a nice portion of vegetables that he likes, lean meats, fruit, and things like that. I also try to always add in a little dessert too. Maybe some pocky or a couple pieces of candy.
He really likes the variety he gets from Bento lunches and being able to have lunch everyday even if he cant leave work for a lunch break. And I can feel better knowing that he is atleast getting a little better of a diet since I make two of his meals a day. Now if only I can get that breakfast thing taken care of.
I would say definitely find out what things he likes and work with that. Soup can be a really great lunch, as long as it has some veggies in it. And then adding some other stuff on the side to make it more rounded. Like my boyfriend only likes cooked vegetables, so that's how I prepare them. And I make him give me feedback on new things I put in his lunch so I really know what he likes.