Mahroosh is a great place, especially if you're on a budget. You should know that they don't serve Shawarmas until after 6pm, I think.
I used to live in Abu Dhabi for four years, and this was a go to place any time. I'd take anyone who visited me there too.
Grape leaves, chicken shawarmas, falafel sandwiches are all great options.
It is tucked away a bit, so you do have to go looking for it, since it's near the Corniche, but not visible from the Corniche.
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