Sweetgreen is the first-ever unicorn salad start-up, luring lunchtime lines across the country with its millenial- and Gen Z-friendly $12 salads. Now ,the brand that brought the farm-to-table trend to fast-casual dining wants to be "the Starbucks of salads."

"If I had told you 25 years ago, when Starbucks only had a few locations, that someday it would be a global phenomenon … nobody would have believed that. ... But, that's what happened," Sweetgreen investor and billionaire Steve Case told CNBC. Today, Starbucks has a market value of nearly $90 billion. "And so that's what we feel with Sweetgreen."