i also just started working in this neighborhood (57 & Mad.) and have found lunch to be a struggle. i often head west, which would be too far for you, but do go your way sometimes. Fusia at 56th and Lex. is decent, if not confused about its own identity.
elsewhere, have you tried Brick Lane Curry on 53rd bet. 2nd & 3rd? there's also a place called Little Thai Kitchen nearby, but i haven't tried it yet. Grand Sichuan is on 55th & 2nd. Korea Palace is on 54th & Park.
I order from Luscious Thai on 60th/1st. Not amazing but considerably better than the other Thai options I've tried in the area. Beef Fried Rice done extra spicy has nice balance of sweet, sour and spicy.
Avoid the larb like the plague however, no one in Manhattan seems to want to make it out of ground chicken and just makes it with minced/diced chicken, utterly terrible tasting. Someone prove me terribly wrong please on that one.
i doubt there is much there, as Manhattan is a desert when it comes to Thai food...but the Thai Consulate is not far away: you could don a Buddhist robe, sit out front, and ask for a taste from some staffer's lunchbox...that's what i'd do anyway...*smiles*...
Alternately, you could stake out the consulate and follow the staff and see where they eat...
Whatever you do, avoid Pooket Thai on 2nd Avenue between 51st and 52nd street. I had the second worst meal of my life. I ordered the pad thai lunch special for takeout. I'll give you the short version of this horror. I waited 30 minutes for the order even though the restaurant was empty. I asked for water as I waited at the bar and received a glass of ice water in a dirty glass. I finally received my food and my lunch hour was nearly over.
Good thing I checked the bag before I left because they forgot the soup. Bad thing I didn't see they forgot the salad. I get back to my office and taste the soup. It is a thin and excessively salty, nasty bouillon cube disaster. I try the pad thai, which turns out to be an unappetizing GREY color, gloopy with sugary sauce and teetering on the edge of disgusting. As I am eating, my chopstick comes across a shard of plastic approximately 2 inches long by 1 inch. I stop eating and throw the dish out.
Just for reference, the worst meal I ever had was at a Greek diner in Jamaica, Queens, where I was served a green burger. I am not talking about a vegetable burger.
Good luck, I think that Thai food, with two exceptions, in Manhattan is quite sad.