the term "lasagna" is indeed a name of pasta, just like "spaghetti" or "tagliatelle", a name given for the flat sheet which is used for this well known dish. So you can put anything you fancy in between, it doesn't need to be tomato based sauce.
the most popular way is to use the bechamelle in place of tomato sauce, with broccoli, asparaguses, spinach or various mushrooms and such for filling. Then you can also experiment with cheeses in between too, anything that melt smoothly can be used.