Pat the flat iron steak dry
Season both sides with salt and pepper
Let the steak sit at room temperature for 20 to 30 minutes
Heat a heavy skillet or grill over high heat
Add a small amount of oil to the pan if using a skillet
Place the steak in the hot pan or on the grill
Cook for 3 to 5 minutes per side for medium-rare, depending on thickness
Flip only once
Check for doneness with a meat thermometer if desired
Remove the steak when it reaches your preferred temperature
Let the steak rest for 5 to 10 minutes
Slice against the grain
Serve immediately