Fuloon in Malden, MA, is probably Boston's most well-known best-kept secret. There are many more great things on the menu (try and stick with things off the Chef's Specialties and Northern/Sichuan sections), but here are a dozen of my favorites to get your started.
'Fuloon' on Serious Eats
If there's one takeaway that's stuck with me since my trip to China last Spring, it's that vinegar and pickling are fundamental to Sichuan cuisine--at least as fundamental as the chiles and heat that food is so well known for. It wasn't until that trip that I made a connection about a bunch of my favorite dishes at Fuloon, arguably one of the best Chinese restaurants in the Boston area: They've all got a sour component.