Having had an Australian born HK boss ( my first full time job ) when I worked for Sony in the 80's and being located 50 metres from Melbournes China Town, I got a pretty good appreciation/understanding for the Chinese food for lunch during those years.
So when it came to living in Hong Kong, I was already pretty familiar with many of the popular items that HK does well.
For me, Char Sui faan ( BBQ Pork ) served with bok choy was always going to be my all time lunch time favourite with Sui Yuk faan ( Crispy Pork Belly ) coming in as a close second fave. I also got introduced to the once a week Yum Cha after work on a Saturday for a bit of Dim Sum, when shops shut at 12:30pm ( in Melbourne ) and we'd venture down to the Shark Finn Inn in China Town. For some reason, an ice cold can of classic coke, to accompany this dish, seemed to be the best palate cleanser and just works well. It's the only time I drink the stuff outside it being used as a spirit mixer.
Because of that experience ( indoctrination ? ) in Melbourne, when we lived in HK, I made it our usual Wednesday morning ritual in Sai Kung, to have Yum Cha, with a couple of SK mates who also appreciated a bit of cha. I am pretty sure over the years we pretty much ate everything that was offered on the menu including Fung Zao ( chicken feet) pigs ear/intestine and so on and enjoyed every bit of it.
So, what are your fave goto HK dishes ?