On the whole, I would advise against eating South-East Asia food in HK. It just doesn't taste the same. But if you are really desperate, try hitting Sheung Wan. We chanced upon Malay Mama because Katong was closed on July 1st at 5pm.

Laksa - definitly better than Katong's, but still not lemak enough
Bak Kut Teh - supposed to the Klang's style with thick soup. Average.
Prawn Noodle - definitely better than Landale's "famous" prawn noodle.
Hakka Yong Tau Foo - Very authentic
Curry Chicken - Don't understand why it is in dark sauce. Can be better
Cuttlefish Kang Kang - The BEST !!
Barley water - very authentic
Kaya toast - Nice touch!

I would pop by for a cheap dinner after work when I'm around the area. Anything from the menu is good to try and it's good to be able to eat this relatively authentic malaysian food.

The laksa is not too bad, though they are always fighting for business from the laksa stall opposite. The lady boss is always accommodating and nice to ensure you come back for more! Must have hong kong milk tea to accompany your meal ok?