This recipe from Delish looks tasty: it's a sandwich of grilled flank steak and grilled onion, plus tomato and arugula. The marinade they suggest is similar to the one I use, except mine includes red wine and does not include balsamic vinegar.
Here is another good-looking recipe for grilled flank steak. Want a more exotic recipe for grilled flank steak? Try this one with Moroccan spices.