Pat the flank steak dry
Season generously with salt and pepper
Optional: marinate for 2 to 12 hours
Preheat a grill, grill pan, or skillet over high heat
Lightly oil the cooking surface
Cook the steak 4 to 6 minutes per side for medium-rare, depending on thickness
Use a meat thermometer if desired; aim for 130 to 135°F for medium-rare
Remove the steak from heat when it is 5°F below your target temperature
Transfer to a cutting board
Rest for 10 minutes
Slice thinly against the grain
Serve immediately