4 days in LA
If I had four days in LA and wanted to experience the best ethnic food, these are the can't misses:
1) Chinese - LA has the best Chinese food in the entire world, never mind the U.S. You must go to the San Gabriel Valley. There are dozens of terrific restaurants: NYC Seafood and Har Lam Kee are two of my favorite Hong Kong style places but there is every type of Chinese regional cuisine available.
2) Japanese - LA also has a tremendous variety of Japanese restaurants. You can have sushi, sashimi, tonkatsu, noodles, japanese curry, etc. Little Tokyo downtown or the Sawtelle corridor on the westside offer many possibilities.
3) Middle Eastern Food - A fantastic selection is available. My recommendation would be Carousel, with locations in Hollywood and Glendale.
4) Thai - Again, we have a great selection of Thai places. East Hollywood's Thai town has a half-dozen great restaurants and dozens more very good ones. I like Rodded and Krung Tep.