The first year I spent in Hong Kong as a student I told myself it was impossible to be a vegetarian. The restaurant menus confirmed it too.
But it is possible. For those looking to make the switch here's how I did it. The Buddhist Chinese restaurants are our best allies. Harvester and Green Veggie in Sheung Wan and Bijas in HKU are great weigh-and-pay places. The food is healthy and tasty too. A decent sized portion costs 45-60 HKD. There is CS Vegan in TIn Hau, which I haven't visited yet. I wasn't thrilled the first time I ate at a Buddhist restaurant as it was new to me. But I find these are the kind of restaurants you can eat at regularly. You can look up these kinds of restaurants on Openrice.
Some other cuisines/ options are: Thai = curry with rice; Pad Thai, flat noodles; Italian = pasta and pizza; Indian and Nepali = lots of options here; Burgers, sandwiches and salads = Pret manger, Grove Cafe and Veggie Monster. Other cuisines in HK like Mexican and Turkish also have veg dishes. The only exception I've come across is Vietnamese restaurants, which seem to have meat in all their dishes.
Popular restaurant chains like Tsui Wah, Fairwood and Eat Together have vegetarian dishes too.
There are thousands of restaurants in HK and most of them have one or more vegetarian dishes. It makes ordering a lot easier!
Ultimately, I cook Indian food on the weekends and learn new recipes from watching vegan Youtube channels. They seem to have innovated a lot given their dietary constraints.
I hope this helps!