Easy:
for dumplings (but the noodles with spicy sauce are amazing):
Din Tai Fung - Arcadia, CA
for dim sum (there are some better places but this is classic Hong Kong style):
NBC Seafood Restaurant - Monterey Park, CA
for Vietnamese catfish:
Phong Dinh Restaurant - Rosemead, CA
I lived in San Francisco and have been to China four times. My fiancee is from Hong Kong and has been all over Asia and the US. San Gabriel valley is the closest you'll get to China outside of China.