Burrito Mama will launch at the end of October on the former Sumo Salad site, and will have a shack-like appearance with a brightly-coloured decor.
As well as a takeaway offer there will be room for 30-covers, with customers able to order Burritos from one of the Burrito Mama team, or via self-service screens, and pay while the burrito is being prepared.
The group is also building an app allowing customers to order a burrito from their desk (or wherever they happen to be) and jump the queue.
It is thought that if the first Burrito Mama site is a success Wahaca, which opens its 11th restaurant on the first floor of One New Change shopping centre at St Paul's in the autumn, will look at further rollout opportunities in the future.
Both concepts will join a host of restaurants and bars at One New Change, including Jamie Oliver's Barbecoa, Gordon Ramsay's Bread Street Kitchen, Byron, Nando's and Searcy's Champagne Bar.
David Atcherley-Symes, retail leasing director at Land Securities, said: “We are very pleased to welcome Wahaca to One New Change and play host to their very first restaurant in the Square Mile. The restaurant will be a great addition to the mix, catering to local residents, visitors and City workers who are pushed for time and will love the fantastic food on the go.
“It’s a really exciting time to be in the City and the foodie scene is booming. We recently launched a weekly Saturday food market at One New Change which is proving a hit with visitors and taking the City back to its retail roots seven days a week.”
Wahaca, founded by Thomasina Miers and Mark Selby in 2005, recently secured its 12th site in Great Portland Street, London. It is believed to have taken the Quiksilver unit for an opening, subject to planning and licensing, later this year.
The company believes it can eventually grow to an estate of between 15 to 20 restaurants in Greater London.