Nearly 25 years ago, Roberto Torres moved from the Mexican state of Guerrero to Orange County, landing a job as a dishwasher at a Vietnamese restaurant.
Torres was part of a tide of immigration from Mexico and Vietnam that has transformed the central section of the county, where Asians and Latinos are now the dominant groups.
Torres found Vietnamese specialties served at Song Long — fish stew, herb-marinated chicken — a little bland. But he rose over the years to become head waiter.
“Chao anh. Chao chi. Anh chi thich an mon gi hom nay?” Torres says, greeting a fashionable couple from Santa Ana, the man in a suit and dark silk tie,...