Costco flat meat cut
Gear mentioned in this thread:
Is it flap meat?
In that case, do as teamfat suggested in his first post. Grill hot and do not cook through - hopefully you don't mind eating meat medium rare or medium at the most, because it will become tough if you overcook it.
And perhaps most importantly, cut thin slices against the grain, so perpendicular to those white fat lines you see on the photograph - again to avoid toughness.
It's a very good cut when prepared well, I would at least give a small piece another chance on your grill before you return it. Best of luck to you!
I say that at Costco here in the middle of the desert, I wasn't sure what it was, but I was thinking something like Flank... should excellent for fajitas, tacos too.
oh and @Lanikaigirl ALOHA! WELCOME to CT from your neighbor in Kaneohe!
I think teamfat was onto something. How thick was it? It could very well have been brisket flat. That's not something you can cook fast. Errr unless you grind it into burgers or something.
I have definitely seen brisket flat at costco (and only flats) They don't do whole packer cuts at any costco near me.
Flap meat is skirt steak not a brisket flat. It's much thinner. I have seen this at our Costco but the cost here is closer to $8 a pound while Prime packer briskets at Costco are still running around $3.80.