"It's a tad crispy on the outside, and inside, it's still chewy. When you bite into it, (the ramen) separates in your mouth, rather than in your hand," Shimamoto, 39, tells CNN of his ramen buns.

Those buns then sandwich a juicy beef patty on a bed of arugula. To finish, they're topped with a generous sprinkling of scallion.

"I can't tell you any more about that," says Shimamoto of his global hit.

"Because that's my trade secret."

Use your noodle

So, how did Shimamoto's love affair with ramen begin?

The Los Angeles native visited Japan with his parents throughout his childhood.

"Every region had a different style of ramen. That really intrigued me, and I wanted to learn more about it," says Shimamoto.

After graduating from the University of California, Shimamoto entered the mortgage industry. But after the subprime-mortgage market crashed in 2007 he "jumped from bank to bank."

"In my spare time, I would go and eat ramen around Los Angeles," he says. "It made me think that maybe I needed a career change."

"I didn't know if I was going to own a ramen shop, or become a big-time chef," he says. "But I knew that I had to do something (related to) ramen."

Tokyo calling

Shimamoto spent four years in Tokyo, managing three different ramen shops. During this time he also took a month off work to travel, making his way from Hokkaido, the northernmost Japanese island, to Kyushu, all the way down south.

"I once had 55 bowls of ramen in 28 days, in 21 different cities. That kind of changed my perspective of what ramen was like," he recalls.

Within the space of a year, Shimamoto had eaten some 600 bowls of ramen. His favorite? Tokyo-style shoyu ramen, which has a soup base flavored with soy sauce.

"There's a nostalgic aspect to it. It was the first ramen I had ever eaten as a kid in Tokyo," he says.

"It always takes me back to the same place. That clean shoyu chicken, and light broth."

His real inspiration, however, didn't come in a bowl.

"In Tokyo, there are food stalls that sell 'ramen burgers'. It was chashu pork (Japanese-style marinated pork belly) sandwiched between noodle buns," Shimamoto recalls. "I remember trying it ... and (the ramen burger) just kind of fell apart in my hand."

"Being from California, to me, a burger is a hamburger with beef, instead of pork," he says.

Shimamoto began toying with the idea of crafting the perfect ramen burger by adapting it to American palates, as well as improving its texture and consistency.

"(Moving to Japan) sort of changed everything. I felt like my life was devoted to ramen."

A food trend is born

In 2012, while living in Japan, Shimamoto was featured in "Ramen Dreams", a short documentary that screened at the NYC Food Film Festival that year.

The picture won best short, and solidified Shimamoto's reputation as a ramen expert.

The following year, he moved to New York City and began experimenting with the ramen burger.

"I had it in my head that I would mess around and try to make a bun (out of ramen), but ... never thought it would become a business," Shimamoto says.

With the recipe perfected, Shimamoto posted about his new creation on his blog a few days before the ramen burger debuted at Smorgasburg.

It went viral.

"The night before Smorgasburg, (the TV show) Good Morning America called and said they wanted to put me on the morning show that day -- before we sold the burger.

"It was a crazy time."

The burger sold for $8 a pop at the food market and was a runaway success.

Ramen dreams

Shimamoto's noodle creation became a mainstay at Smorgasburg and its success spawned similar ventures around the world.

He says he's heard of ramen burgers popping up in Canada, Australia, the Philippines, Singapore and Germany.

But he doesn't own the rights to those recipes.

"It's very difficult to patent a recipe," he says. "I didn't see a point in paying for trademark fees. It's flattering that people copy it ... it doesn't hurt me at all."

His goal, he says, is to make quality ramen and share it around the world.

Varieties include shoyu, shio (sea salt) and tonkotsu (creamy pork bone broth) varieties -- Japan's most popular ramens -- alongside more unusual specialties, such as the sabatino truffle shio, featuring truffle oil as the star ingredient.

There is also a teriyaki pulled pork burger that's topped with yuzu coleslaw and teriyaki sauce.

"This is where I get to showcase what I can do with my ingredients," he tells CNN. "It's really just me testing and learning about ramen every day. Making something new, then creating it into the perfect bowl for customers."

He also runs a wholesale business, making ramen soups and ingredients -- such as toppings -- for other shops and restaurants.

Previously, Shimamoto ran now-defunct restaurant, Ramen Co. in New York City, which had an outpost in Los Angeles.

"Because of the ramen burger I was able to build separate businesses that have taken my dream a step forward."

Ramen is life

The ramen burger reflects Shimamoto's journey as a Japanese-American.

"The two cultures I grew up in feed into the type of food I've been making," he says. "I'm trying to make food that tickles my memories, and my childhood."

This is evident in some of the more unusual combinations.

You'll find east-meets-west hybrids like the fuji pineapple burger, which combines grilled pineapples, shredded lettuce, and Kewpie mayonnaise.

"Ramen Shack is ramen from my own personality," he explains. "When people come to eat it, they taste my experience -- the different bowls I've learned (about) over the years, and how my passion has turned into a bowl of ramen."