After doing search on the internet, I finally settled on the recipe from Bonbon Kitchen. The recipe is in Chinese, if anyone needs the recipe in English please leave a comment.
There is no sugar in the marinade but I think adding a tablespoon will balance out the saltiness of the fermented soy bean paste (main marinating ingredient).
Charsiew rice with stir-fried vegetables on the side. Char siew was delicious although I would have prefer more sauce; will increase the marinade next time so yield more sauce.