Just a bump to this thread to say thanks for the tip-off about black lime powder, Ghoulie. I haven't tried the shwarma yet for reasons of Christmas / in-laws staying, but I plan to have a go this weekend.
I did order some black lime powder though and it has transformed several things that I have cooked. Just one example: on Xmas Eve we were invited out and asked to bring a "salad with no lettuce or tomato". I finely sliced fresh fennel with very thinly-sliced lime and lemon juice and good olive oil; tossed in some pomegranate seeds and diced walnut; seasoned with salt. Hmmm...good but not quite....so I tried a sprinkle of black lime powder and it went into orbit. Three people have asked me for the recipe. I have warned them not to try it without the black lime.
Cheers,
Tim