I think your only option these days in Sai Kung, now that the Hong Kong Burger Company which was the best Burger place to date, closed a couple of years ago in sk square, now you've just got Burger Deli located in post office alley, which is just a hole in the wall sort of deal with a couple of outdoor tables and chairs, not sure if they ever did or do coleslaw.
Jaspa's in the same square, might do a sit down burger as the same restaurant group (Castello group ) owned, The Hong Kong Burger Company. They serve salads, chips and alcohol. Ask them, they're pretty accommodating.
http://casteloconcepts.com/our-venues/piccolo039s piccolo does a very good burger on a timber board for about $125, the last time I was there. again, part of the Castello group. quite substantial, you should like it and they serve alcohol, salads and chips.