There are several Suan Long restaurants in Zurich. My favourite one is at Stadelhofen railway station. When you come in there is a take away counter with ready made meals or they quickly prepare the dish you order. There are also a few tables for a quick meal. In the back section there is a proper sit down restaurant where you get served. The restaurant is wheel chair accessible although there is not much space. The toilet is not wheel chair accessable as it is up a staircase on the upper floor, but I guess you could use the one in the railway station area.
My favourite dish is Singapore noodles. I’ve had them in both sections of the restaurant. The spicyness varies.