After months of delays (the restaurant was originally due to begin trading in July) Fonda Mexican's sixth venue - and first outpost in the north - is ready to open.

It's the same deal as the chain's other venues - fast Mexican food in a playful space, and it follows the same design concept as its siblings: approachable, fun and relaxed. Fonda picked Melbourne design firm St Style to do the fit-out. The building, which is on the corner of Smith and Stanley Streets, used to be home to the Mr Cheesecake shop.

Stephen Mooney, St Style's Creative Director, says the refurbishment was "an incredible challenge from the very beginning. The dilapidated cheesecake factory was always going to be a struggle."

In late November, for example, Fonda site workers hit a gas main and nearby buildings had to be evacuated.

"A ton of underlying issues with the building were revealed during the demolition phase of the project, as well as a couple of stunning surprises," says Tim McDonald, one of Fonda's co-founders. Those revelations included original timber beams in the upstairs ceiling, a concrete stairwell, a pink brick and teal tiled fire place, pink brick walls and an archway in the upstairs hallway.

"We desperately wanted to retain the heritage soul and charm of both buildings," he adds. To do that, they had to redesign and shuffle the original plan for the interior layout multiple times.

"For example, when we stripped the ground floor walls we discovered two huge stunning original steel lintels that we wanted to highlight in the front dining area," he says. "This meant we had to redesign the positioning of the new Stanley Street window we've installed and restart the approval process with council."

Fonda and St Style were keen to create as much visibility in and out of the corner building as possible, so the design includes numerous large windows along Stanley Street.

St Style collaborated with design studio Wild Hen on the pastel colour palette, which extends to the unmissable artwork on the Stanley Street facade - a building-wide geometric mural by artist Deams.

The interior is retro but contemporary, with exposed brickwork, and concrete and timber finishes. There's a colourful neon installation on one of the walls and geometric furniture. A void was cut into the first floor to join the downstairs to the upstairs, where there's now a terrace bar.

"It's been such a fun project to work on, particularly because the area has an eclectic style of architecture and culture," says McDonald. "Smith Street has become one of Melbourne's top dining strips. We're really proud to be a part of it."

Fonda Collingwood opens to the public on January 13, 2017.

This article was updated on January 13, 2017.