Asiana, ANA and United have Los Angeles LAX to Ho Chi Minh City, Vietnam SGN priced at $558 round trip for one-stop flights via Seoul, South Korea for travel from mid August to April 2018, December dates excluded.
Hanoi, Vietnam HAN is $608 with Asiana for this same travel period, however, SkyTeam member China Airlines has $550 round trip tickets.
United Airlines ticket for ANA operated flights
Los Angeles LAX – Tokyo NRT – Ho Chi Minh City SGN – Tokyo NRT – LAX
Expedia.com ticket for Asiana flights
Los Angeles LAX – Seoul ICN – Ho Chi Minh City SGN – Seoul ICN – LAX