Westminster is majority Vietnamese in population, like Garden Grove
Plurality yes, but definitely not majority.
Persons of Vietnamese ancestry are the lone Asians who come close to voting Republican (as a group), and both of these areas reflected that fact in 2020 by moving sharply towards Trump.
Garden Grove, CA demographics and election results
Westminster, CA demographics and election results
Nowadays the rest of once-nice Orange County -- up through the 1980s or so it was the ultimate paragon of conservatism and was therefore reviled by the media and other liberals -- doesn't do nearly as well as these 2 cities, but there are still some good areas.