For Restaurant which serve oyster as well, you can go to Sai Kung. I have been to this one, it is good there.
全記海鮮
新界西貢海傍街51號地下
電話:2792 6183 傳真:2791 6742
For Western food, you can try to go to
RED - Bar + Restaurant
Shop 3082, 4012-18
Telephone
(852) 8129 8882
http://www.ifc.com.hk/english/restaurant.aspx?id=4018
Or similar in IFC, there is another called
ISOLA bar + grill
Shop 3071-75, 4011
Telephone
(852) 2383 8765
http://www.ifc.com.hk/english/restaurant.aspx?id=3071
Alternatively you can go to Stanley
Boathouse
86-88 Stanley Main Street,
Tel:2813 4467 Fax:2810 4467
Enjoy!