Place 2 tablespoons of peanut oil and heat until almost smoking.
Split the piece of ginger open with a knife then whack it with the flat side of the knife.
Lay the ginger pieces in the oil, cut-side down to let it start to perfume.
Pan-fry the bok choy, cut-side down, for a couple of minutes to give it some color.
Add the water and cook another minute to steam the bok choy; carefully remove it to a plate.
Add the soy sauce, oyster sauce, lemon juice, and brown sugar.
Cook and stir for 3 minutes until the sauce is the consistency of syrup.
