More than a third of the population is Hispanic, and Asians make up nearly one-fifth of the county — a growth of nearly 40 percent in the last decade, according to the new census. In some inland cities, like Buena Park, Fullerton and Anaheim, the vast majority of the population is Asian or Hispanic.

“My son is the only Mexican kid I know who says he wants rice and beans when he really means edamame and sushi rice,” said David Gonzales, 39, of Fullerton, a new fan of Dos Chinos, referring to his 3-year-old son, Jackson. “He eats food I never tasted growing up.”

When he started his mobile business, Mr. Phan said his parents just “laughed like you wouldn’t believe,” telling him their friends “would never want to eat here.” And really, they don’t.

But Mr. Phan’s truck is particularly popular with the under-30 set: people who may think that sriracha-tapatio-tamarindo cheesecake is not all that unusual.

Some of Mr. Phan strongest memories of life in America are food-related. There was the country fried chicken during his family’s brief stay in North Carolina when they first immigrated. And nopales (cactus leaves) and ceviche, raw seafood marinated in lime juice. He laughed, almost embarrassed at his admission: “What we thought was adventurous is just normal now.”