Whisk together all the ingredients for the sauce in a bowl until completely smooth. Set aside.
Prepare the meatballs:
Gather the ground chicken, minced garlic, ginger, shallot, tamari, and egg into a large bowl. Use a rubber spatula to mix until completely incorporated.
Add the panko and mix with the spatula until combined.
Form the mixture into tablespoon-sized meatballs. The meatballs may feel soft and not be perfectly firm, and it’s okay if they’re a little ragged around the edges. Transfer to a plate and refrigerate for 10 minutes.
Fry the meatballs:
Meanwhile, add 2 tablespoons neutral oil to a wide pot over medium heat. Allow the oil to preheat for 5 minutes as the meatballs refrigerate.
Add the meatballs to the pot, cooking in batches if needed, for 3 to 5 minutes per side until browned on all sides. Transfer to a plate.
Simmer the meatballs:
Carefully wipe out any excess oil from the pot. Return the meatballs to the pot and pour the sauce on top. Turn the heat to medium-high. As soon as the sauce begins to bubble, reduce the heat to low and cover. Simmer for 20 to 25 minutes until the meatballs reach 165ºF when pierced with an instant-read thermometer.
Finish the meatballs:
Remove the lid from the pot. Add the white parts of the scallions and the chopped yu choy along with a pinch of salt. Cover and simmer for 5 minutes until the greens wilt and the sauce loosens up from the water released from the vegetables. If the sauce is too thick for your liking, add a splash or two of water after simmering. Taste and season.
To serve:
Spoon the meatballs over cooked white rice. Serve with the reserved minced scallion greens and sesame seeds on top. Enjoy!