List away with any street food or virtually hole in the wall institutions that you know. The only places that I consistently pass are a set of stands on Brixton Station Road and a meager (and quite expensive) arrangement on Goodge St. The former has 3 Jamaican carts, a Jamaican kiosk which does excellent business and has very high turn over among locals, a Portugese cart that makes fresh griddle cooked breads which are opened, lathered with herb butter and then sliced like a sandwich (a whole lunch for 2 quid if you like bread.) I've been meaning to try a Ghanan stall that I keep passing in one of the markets. It usually has at least a few people eating at any given time that I pass (I'm not exactly there for lunch time or dinner time so that seems like OK turn over.) The Goodge spot has a Thai stand which always has long lines, a Chinese stand which does OK, a crepe stand which is dead, a salad stand which is worse than dead and a burrito stand which occasionally has a sign of life. The burritos are -VERY- expensive (I would underline, make that red and italicize it if I could.)
I would be especially interested in Hispanic fare though I have doubts about being able to get it.