Grilled Flank Steak on a Bed of Roasted Peppers and Onions

I wish I could remember the precise origin of this recipe. It came to me as a taste memory of the full flavors of grilled beef, roasted peppers, and balsamic vinegar. The beef is marinated briefly in the vinegar with a little olive oil, and the sauce is composed of roasted peppers and onions seasoned with a bit more vinegar and olive oil. As you may know, balsamic vinegar, a specialty of Modena, has a round rich taste and is not at all sour. It is as mellow as a good wine and adds a wonderf