This is really simple. What do you like in a salad?
What dressing do you like? Stick that into a bento box.
Here's what I usually use:
Iceberg and/or romaine lettuce
Roma tomatoes cut into chunks
Ranch dressing, Benihana ginger dressing, or
Naturally Fresh ginger dressing
Yeah, my salads are pretty simple and probably boring,
but I like 'em. If you eat enough green salads to know
what you prefer, then it's pretty unlikely you need
a recipe to help you make it.
A few packaging-related notes. One, if you're packing
a salad as part of a larger meal, the rest should be
eaten cold, or you should be able to take the heatable
stuff out easily to microwave it. (Otherwise you either
have to messily take the salad out or heat it up. Blah!)
Second, I recommend putting the salad dressing in a
separate little container, especially if you have things
other than salad in the box. Otherwise, it'll end up
all over the inside of the container.