The vegetables must be rid of their high water content before they are added to the meat filling. The high water content would have made the filling too watery, and some of the bitterness can be removed by squeezing out the water. The napa cabbage was chopped and salted and the Shanghai bok choi was blanched in water and then chopped. I found the potato ricer to be such a handy tool to remove the water from the vegetable fillings. I used to always use my hand to squeeze the vegetables, but it always left too many bits and pieces on my hands, and there would have been too much wasted. You can see the difference in the volume of the vegetables (Lower left and upper right are the bok choi and napa cabbage before water was removed. Lower right is all the vegetables combined with water removed.)
Another handy tool is my KitchenAid mixer! The meat and shrimp should be stirred long enough to develop protein strands, which help to retain additional liquid. I normally would have added water that's got ginger and scallions mashed up and strained. But I happened to have ginger and scallion oil sauce in the fridge, so I just added a big spoonful of that. I also added salt, white pepper, and some mirin.
Aren't they cute? They look like little cute packages!