From Harvard Square, go to Watertown and check out Little Armenia – just keep going up Mt. Auburn St. until you come to a number of Middle Eastern and Armenian markets. One of them is Eastern Lamejun bakery (though actually, that might be before you get to the real concentration of stores). In any case, you’ll want to try lahmejuns (like small pizzas) and related turnover-like foods (notice a theme here?). You can also get good feta, olives, taramosalata, etc., etc.
Excellent recommendation! I grew up in Watertown and grew up eating lamejun and turnovers & stuffed grape leaves every 2nd or 3rd Saturday.