Is any time not taco time? No, says Taco Time, a US chain of Mexican restaurants founded in 1959, and which is not the subject of this article. A small tortilla folded around a filling can be enjoyed at any time of the day, and if it happens to be dinner time, you can get over the taco's intrinsic lack of size simply by eating many of them. A taco can be filled with meat, fish or vegetables or even be fully vegan, and still be authentically and undeniably a taco, in a way which is simply not the case with a burger or hot dog. Such is the life-giving power of a simple taco that in the deplorable 1974 action comedy Freebie and the Bean, in which hothead cop James Caan (Freebie) and his similarly short-fused partner Bean (Alan Arkin) brawl and car-chase their way across San Francisco, the ethnically Hispanic Bean is revived from an apparently fatal gunshot wound only by the prospect of Tex-Mex snack food. 'I gotta have a taco', he gasps, causing his grieving partner to snap out of his funk and the pair to launch into yet another quasi-hilarious fistfight.

Yes, tacos are the very bread of life, especially when topped with the chipotle salsa of good company, the avocado of memory, the pickled onions of appetite and the grated cheese of can-I-have-some-more-grated-cheese-please. Which brings us to the secret which we reluctantly share with you: the folks of Wahaca Edinburgh, who are opening a new taco joint in the capital next month, are parking their taco van in St Andrews Square this weekend and handing out – wait for it – free tacos, to the accompaniment of live music from Brass Gumbo. Yes, free tacos. A taco, in return for nothing.

Do not ask what you did to deserve this good fortune. Consider that the wheel turns, we all rise and fall, and one day's free gourmet taco is another day's under-filled and scantily-garnished chicken breast on wheat bread. (Why won't you answer our emails, Subway? Don't think that vouchers will make it better. We have a new friend now.)

The Wahaca van is in St Andrews Square, Edinburgh from noon--3pm and 6–8pm on Fri 30 Sep, and noon--5pm on Sat 1 Oct. Wahaca opens its Edinburgh branch on Mon 10 Oct.