The combination of arugula and basil makes this the perfect summer salad. You can also add other greens of your choosing or edible flowers, such as nasturtiums. Flank steak works best here as well because of its rich flavor.
Discard the stems from the basil and arugula. Wash and spin dry the leaves. Transfer the greens to a large salad bowl with plenty of room left for tossing. Season the flank steak with salt and pepper and grill or sauté the flank steak.
Slice the meat across the grain, tilting the knife as you slice in order to maximize the size of the slices. Slice as thinly as you can. Put the slices on the greens.
Drizzle the vinegar and oil over the salad and season with salt and pepper. Toss and serve immediately, distributing the steak slices so everyone gets a fair share.