Honestly all the cali cities have pretty diverse food options, it's just that the cities are known for certain foods. If you want a specific cuisine, chances are there's still a restaurant nearby for that, granted you live in the big cali cities.

LA imo is known for korean food in ktown and street tacos but also has a lot of organics and vegan options. There's also sawtelle and little tokyo with lots of Japanese food options. There's even a decent strip of greek, persian, turkish food options.

Irvine (and Westminster) is known for mostly viet food imo

SD has a lot of coastal dining and surf n turf options

SJ is also known for viet food and mexican food but also has a sizable portion of cantonese banquet style restaurants and japanese izakayas

SF has a lot of chinese food (cantonese, taiwanese, mainland) due to the chinatown and also lots of fishery based restaurants near the ports. Japantown there is also pretty sizable and includes a variety of japanese foods.