This non-Korean likes the Yellow Vendor food truck that operates in DC.
Mandu is a Korean restaurant in DC. I ate there a long time ago and liked it. It appears to be doing quite well: Two locations and plans for a third. I suspect it may be less than authentic, however. Hopefully not as inauthentic as Ping Pong Dim Sum.
I don't live in Boston, but my sister does. For a first time Boston visitor, I recommend a lobster roll from James Hook, a cannoli from Modern Pastry, and dumplings/hot noodle soup from any one of many restaurants in Chinatown.