There must be a dozen "Mongolian Grills" in suburban Detroit.
( Chinese buffet + a grill for selected ingredients )

On one visit I picked;
thin sliced beef, green peppers, onions.
Hmmmm.... tastes just like a Philly steak sammich.

Next trip, I brought a couple of pre-sliced hoagie rolls.
Got my plate of grilled beef ( mushrooms too )
Filled the hoagie roll, and enjoyed one of the best
steak sammiches I've had in a while.

I must admit, the waitress was a bit suspicious....
but she did find a bottle of catsup for me.