Thanks to Fiona, I was told that it's pickled lettuce (菜心) & XO sauce, so I came home & mix my own.
To make this, I bought Narcissus Brand Pickled Lettuce (菜心) & Lee Kum Kee Extra Spicy XO Sauce, and I began mixing it.
2 cans of Pickles Lettuce, drain the excess water in the can
Diced into cubes or smaller pieces
6 spoonful of XO Sauce
Mix evenly; store in airtight container & keep chilled.
Tested; although it doesn't taste exactly the same as what I had at Lei Garden, it taste quite good. It can be eaten on it's own, add into instant noodle or fried rice.