A former professional tennis coach founded the fastest-growing restaurant in America

Pieology is taking over America.

The fast-casual pizza restaurant is the fastest-growing chain in America, according to data compiled by Technomic.

Pieology has 61 units in 11 states. The company expects to double that number by the end of the year.

Pieology's founder, Carl Chang, told Business Insider the company started when he noticed a problem in the pizza industry.

"Pizza for us was somewhat broken," Chang, who is the brother and former coach of professional tennis player Michael Chang, said. "Pizza used to be a celebration when you were with family and friends ... now it somewhat has become a bit more [of a] convenience food or a coupon food if you will."

Many chain restaurant pizzas were perceived as boring in an era of customization led by fast casual Mexican chain Chipotle.

Chang knew that he wanted Pieology to be an "environment that created inspiration." For instance, there's a quote board in every store that features inspirational quotes. He also wanted the restaurant to be a "celebration of food."

Pieology appeals to customers because it allows them to customize their pizzas (which makes it similar to Chipotle) - from wheat crust to gluten free crust to vegetarian pizzas to dairy-free cheese. There are 40 toppings, and a custom pizza is $8 or less.

Chang calls everyone who comes to dine at Pieology a "pieologist."

Chang uses several different vendors, and he encourages produce to be locally-sourced as much as possible. The dough for the crust is made in-house.

Pielogy also caters to the local demographic and alters the menu for each individual community. For instance, it uses garlic from Gilroy, California, which Chang calls "the garlic capital of the world," in its local pizzas there.

As the company plans to expand to more locations, Chang faces challenges.

He views his competitor to be Blaze Pizza, another pizza chain with custom-made pizzas which threatening some big-name pizza brands. But Chang says Blaze's "goals are a number of units ... I guess that's a qualifier for winning. For me, it's a bit different."

In the future, Chang simply "[hopes] Pieology becomes a brand of relevance. One that's recognized for truly making a difference at the local level."

That's Pieology's secret: keeping the focus on the community and individual while expanding so rapidly.

At the end of the day, Chang - who always will try new variations of pizza but says his favorite is the "base product" (a great cheese pizza) - is simply proud of his business and what it means to him.