I often give dd a choice of wraps/sandwiches in her lunchbox - eg today she has a choice of ham or tuna and sweetcorn. My reasoning is (a) she may be starving and eat them both and (b) it's hard to predict in the morning what you'll fancy at lunchtime, so if she only has one because she fancies that one, fine, if she eats both because she's starving, that's fine too.
I do think it's great that her teacher monitors what the children are eating, but yesterday - she had two wraps in her lunchbox - she went on to her fruit and was apparently told by her teacher in no uncertain terms to eat the other sandwich first.
Any thoughts?