I go to the Nha Trang Vietnamese Cuisine many times. The food there are good and it is easy to go to their restaurants.
Locations of their restaurants: http://www.nhatrang.com.hk/locations/
Two restaurants I have been to:
Shop G51, Ocean Terminal
Phone: (852) 2199 7779
You can see the sea from the restaurant.
Shop 703, Level7,
New Town Plaza I
Phone: (852) 2605 8887
Close to the MTR station. Just inside the New Town Plaza I.