How far are you willing to walk? Meanwhile, here are a couple of threads I came up with:
"What to eat near 35th and 9th?"
"Theatre on West 36th Street [between 8th and 9th Av]-Where do we eat?"
(Of course, you'd have to see which of these places would be open for lunch)
In that case, you really should consider some of the Korean places between 5th and Broadway/6th. You can start by looking here:
"Dinner in Koreatown"
Most if not all of these places are also open for lunch.
Also, though I tend not to think of it as a restaurant, definitely consider Woorijip:
It's more of a Korean deli/steam table place, good and cheap, with tables if you want to eat your food there.
Also, look here:
"Lunch around 1 Penn Plaza"