Best Ethnic in the city...Greek, Thai, Indian???
Looking for good places to eat in Midtown, particularly for lunch???
If you want to stay in Mid-town for real ethnic food then your question is mute. NYC is a city of neighborhoods and if you want experience real ethnic cusine then you might have to go a little farther to venture into real neighborhoods and especially in the Boroughs.
For Greek you might want to give Astoria a try. Demitris is my neighborhood joint but I am sure there are other great suggestions from other Chowhounders.
For Thai, hands down to Sriprhaphai in Woodside. Voted many times as the best Thai in the city. Highly recommended.
As for Indian, I am not sure.
As for Korean, try some of the 24hr joints in Korea Town and in Flushing.
Here's my $0.02
For Lunch go to Angelo's Pizza on West 57th Street. They are related to Nick's Pizza on Ascan Avenue in Forest Hills which is just great. Siciliana salad is fab as well as their thin-crusted pizza. Also China Grill in the CBS bldg. The salads and appetizers are enough to share and the cuisine is always delicious.