If you have had your fill of rice and noodles, there are two western style restaurants in Chiayi.
Calgary's is probably the best, which a selection of the usual American/Italian/Mexican type food..
This is also something of a hangout for the English Teacher/Expat crowd...
The symbol of Chiayi is chicken rice.
The most famous one is fountain chicken rice.
It's just near by the fountain in Chiayi center. Easy to find the to try.
Favorite Dish: Chicken rice is turkey with rice. Chicken are slices with special souce. You can eat it together with fried vegetable, tofu etc. Its taste is light, but you won't forget it.
I would NOT call it a restaurant if you want to try something really nice in Dongshi Town, a very typical Taiwanese little township. Just go and find a food stand and then enjoy your oyter feast. BTW, if you want to try something fun (not on the menu), just ask them for help, they are willing to serve you.
If you want to have some street vendor or pushcart food your best bet is to attend a night market in Chiayi. Friday nights head over to the stadium areas on the southwest edge of town, off of Chwei-Yang Road, and you should have a wide choice of vendors. Wen-Hwah (Culture) street has some vendors at night. On weekends you can sometimes find food vendors in Chiayi Park, near the big playground and not far from the Confucian Temple.
Favorite Dish: These days when I visit Chiayi I miss my favorite street vendors, who all seem to have quit the business. If you ever find someone selling scoops of ice cream out of a push-cart in Chiayi be sure to get some. I don't know if the ice cream vendors are still operating, but in the early 1990s pushcart ice cream was the best ice cream you could get outside of the New Taiwan Bakery.