If you want something a bit more authentic, though, I can’t do better than recommending Tayyab’s: New Tayyabs, Fieldgate Street, London E1 | Food | The Guardian. It’s small and crowded, but the food is out of this world. Well worth the wait, and there often is a wait, with the queue going out of the door and into the street. If you can have your meal at a slightly off-peak time, it would help avoid a long wait.
Tayyab’s is great (as long as you’re not vegetarian). If there are enough of you make sure to book. I felt like I was in Goodfellas as the waiter walked us past the long queue to our table!
Looks like it’s gone bust. Shame, as I was going to check it out on your recommendation.
Another place to consider is Wong Kee in Chinatown. Very good, very cheap, simple Chinese food - and astonishingly rude waitstaff. People actually go there just to get insulted.
I heavily recommend a persian restaurant in Covent Garden called Simurgh - it’s in Garrick Street. More info here. Taken loads of people there any no-one has ever had a bad meal.