If you can find it, this brick-domed subterranean cavern makes an appealingly untouristy alternative to the larger Hamam-e Vakil teahouse. It's not quite as atmospheric but food is served for longer hours and at prices that are slightly lower.
Walking from Tohid Sq, turn right at the first charsoq (12-sided passage junction), then turn left at the first alley and look for 'Traditional Restaurant' banners.