Thai Island is a great choice for lunch in the Finance District. They have both thai food and vietnamese food (such as the beef noodle soup ("pho") and dry vermicelli with spring rolls). There is a location in Brookfield Place food court in addition to their original Exchange Tower food court location (the 130 King St W location listed above). They do fast and tasty thai and vietnamese food at a reasonable price - it's possible to get lunch here under $6.
Things to order: Beef Noodle Soup, Pad Thai, Green Curry, Vermicelli with Spring Rolls
Tips: There are 2 lines - one line for the "hot" table where you can order various meats and vegetables to go with rice and noodles. The other line is for ordering noodle soups and dry vermicelli. The noodle soup line is also where you should order their deluxe pad thai that comes with big shrimps. So much better than the hot table food line!