This weekend I am cooking(at a tailgate) for about 30 people. I have only cooked Flat Iron once before and it was great but I don't have time to sear each one individually. I'll be cooking on the grill(propane/ large grill surface). They will be cut up for fajitas as an end result.
I am thinking since it seems to have a great beefy flavor to just play off that with some sea salt, cracked pepper and maybe a little cayenne to add spice.
Probably go with a solid Medium rare -> Medium to satisfy most. I am sure we'll have a few in the crowd that request well done. I guess they can eat chicken.
Any other easy suggestions? Remember this is for a large crowd and not in my kitchen so the difficulty needs to be pretty low, even though we have a pretty elaborate tailgate.