Transfer onions to baking sheet or baking dish with tomatoes and season with salt, pepper.
Roast 8 minutes, then add vinegar and brown sugar, roast further 3 minutes.
Meanwhile cook lasagne sheets in boiling salted water until soft. Drain well.
LAy sheet of lasagne on serving plate. Pile vegetables on top. Cover loosely with second sheet of lasagne, and serve immediately sprinkled with chopped fresh herbs of choice (dill, basil, parsley, chives - whatever!).