On now/has already started, it wasn't advertised prior and hasn't been posted directly on their social media. It also can only be obtained by saying "congrats on the 15 million" when ordering so I'd say there should still be some left at each store.
In honour of the 15 million meals the chain has donated to those in need through its homegrown Plate 4 Plate movement, some of Zambrero's Sydney stores are giving away 150 burritos, each.
If you hop over to Oxford Street, Coogee, Lidcombe, Campbelltown, or Marsden Park, just tell your favourite wrap-assembler / new m8 "congrats on the 15 million" to receive that perfect freebie.
Info via Pedestrian TV
150 per store? Probably all gone by now lol