In case anyone was curious, there is a halal cafe called "Брат" ("Brat", meaning brother) in central Saint Petersburg which serves Chechen food and is advertised occasionally as a "Chechen restaurant". You can read the reviews on Google yourself: https://goo.gl/maps/wLi8qCoP8MaQy9Vv9 "Вкусно, как в Грозном!" ("Tasty, like in Grozny!")
Or on Yandex: https://yandex.ru/maps/org/brat/1450497326/reviews/?ll=30.38... "Нам его посоветовали как «чеченское кафе»." ("It was recommended to us as a "Chechen cafe".")
(There is also another cafe called MaggroZ.)