The easiest way to get them to eat a variety of food is to give them small portions of different lunch options.
This way if they don't like something, there is not much of it that they have to eat.
I call it buffet lunch and the kids love it!!
My rule is if the kids want more of any of the options that they must eat everything first. This way they don't fight eating food they don't like because it's just a little bit and then they can get more of what they want.