Pat the flank steak dry
Season both sides with salt and pepper
Let it sit at room temperature for 20 to 30 minutes
Preheat a grill, grill pan, or skillet over high heat
Add a little oil to the cooking surface if needed
Cook the steak for 3 to 5 minutes per side for medium-rare, depending on thickness
Use a meat thermometer if desired, aiming for 130 to 135°F for medium-rare
Remove the steak from the heat
Rest the steak for 5 to 10 minutes
Slice the steak thinly against the grain
Serve immediately