Stockbridge area places for lunch
There are dozens of restaurants within 15 mile radius which would include Great Barrington, Lenox, Pittsfield so would be easier to answer if more specific.
That being said could consider Once Upon a Table in Stockbridge itself, or maybe Cafe Adam in Great Barrington.
Seafood you won't have much luck, there is Salmon Run in Lee which is quite decent but atmosphere is nothing special.
325 Stockbridge Rd Ste 4, Great Barrington, MA 01230