One of my favorite summer flavors is that of classic sweet-and-sour three-bean salad dressing mingled with the rosy juices of a rare steak. Here I combine the two in a kind of steak and three-bean salad, which travels well to potluck occasions and will make everyone (but especially the meat lovers) very happy indeed. Other cuts besides flank can be used if you prefer, and the steak can be pan-seared in a heavy skillet over high heat on the stove.