“A-B-C-D-E-F-G,” sang Stephen Starr on a recent Monday morning, channeling his 4-year-old self, just loud enough for the workers scurrying to set up his newest restaurant to hear.

“... H-I-J-K.”

He paused.

“Elemenoh.”

He stopped singing. “‘L-M-N-O’ is the part that most kids get stuck on,” he said, counting himself and his own children with mashing the four letters together.

When it came time to name the Baja Mexico-theme bar-restaurant he planned to open in a former marble and granite warehouse beneath the Market-Frankford El at Front and Palmer Streets, he jotted down “LMNO.”

This was nearly three years ago, when the restaurant economy was roaring and Fishtown and Kensington were bursting with big-budget projects such as Suraya, Pizzeria Beddia, and Laser Wolf. He’d already been in Fishtown for years, with Frankford Hall (2011) and Fette Sau (2012).

LMNO — Starr’s 36th restaurant, with a $5 million budget for an open kitchen, skylight-filled dining room, extensive patio space, and an indoor-outdoor bar, all designed by New York tastemaker Serge Becker — was penciled in for an April 2020 debut. But, like many other restaurants enmeshed in months of occupancy restrictions, followed by a general softening of the public’s desire to dine indoors and a labor shortage, LMNO was back-burnered.

It is now due to open Wednesday.

Like most of Starr’s restaurants, the space dictated the concept. “I had several ideas, but I really wanted to work with Serge, and we talked about what we wanted to do,” Starr said. “We thought Mexican, but not the typical Mexican. We were tired of doing that” — see El Vez and El Rey. “We wanted something cleaner — food that a lot of people [in Philadelphia] hadn’t seen yet, and with a casual and fun atmosphere that speaks to the neighborhood.”

“If you’re into Mexican [cuisine], that’s one of the regions you want to focus on,” said Becker, the Swiss-born nightlife guru and hospitality designer whose edgy projects in the aughts included Volume in Williamsburg, Brooklyn, and the speakeasy-style Mexican restaurant La Esquina under a taqueria in Lower Manhattan. One of his early works was Area, one of the original so-called Manhattan hot clubs.

During a tour of LMNO’s building, Becker said he saw elements of Bowery Bar, which he had converted from a gas station a quarter-century ago.

Becker mixes modern materials alongside more rustic ones, including vintage furniture from the 1970s and 1980s. It was his idea to equip LMNO with a retail bookstore, a partnership with New York City’s Dashwood Books, selling avant-garde titles. The alcove has its own dining table.

Such cross-programming is desirable in neighborhoods with a large population of younger people, Becker said.

LMNO is “similar to what we had downtown in the ‘80s and Brooklyn in the ‘00s,” Becker said. “I felt I wanted to connect with that energy. We had a lot of space, and I thought that the type of community that lives there and hangs out there will be culturally interested in something on that level.”

“Music is a young person’s thing,” said Becker. Control of the music has been given to creative director Jason Carroll, whose playlist will cover everything from Arthur Russell to Burna Boy. DJs will be brought in during dinner and brunch on weekends.

There also is a low-lit, intimate listening room, tucked behind a secret door in the back and stacked with classic vinyl and a two-channel analog sound system featuring a pair of Klipsch La Scala speakers and vintage JBL4312 studio monitors that are connected to a Bozak four-channel rotary mixer. (Seems to be a trend with the secret rooms since Jose Garces placed a karaoke room behind the host stand at Distrito in University City a few years ago. The new W Hotel’s lounge on Chestnut Street has a private lounge behind its bar, as well.)

Photography exhibitions, curated by David Strettell, feature Bill Bernstein’s iconic 1970s disco images, taken at such venues as Paradise Garage, the Loft, GG Barnum’s, Studio 54, Xenon, and Ice Palace.

Starr consulted with chef Javier Plascencia, the pioneer of “Baja Med” cuisine, and brought in Francisco “Frankie” Ramirez to run the kitchen.

Ramirez, a Mexico City native, started with Starr as a 16-year-old dishwasher at Washington Square (now Talula’s Garden). He moved up through the ranks, working at Morimoto before turns at Vetri and Bliss. He returned to Starr at Parc in 2008 before leaving to join the now-shuttered Tredici as executive chef.

Ramirez plans to execute what he calls “happy contradictions” of food that’s light but rich, cooked slowly and then fast, clean yet messy presentations, simple while complex.

Think aguachile and ceviches, beer-battered fish, house-made corn and flour tortillas. Custom grills turn out pork for tacos al pastor. Starr said his favorite dish is pescado zarandeado — a shareable whole snapper that is marinated, butterflied, and grilled.

With LMNO on its way, Starr has turned his attention to his next projects: a Pastis branch in Miami; Bankroll, an upscale sports bar in Rittenhouse; and an Italian restaurant and market in Washington, D.C., with Los Angeles chef Nancy Silverton.