Wash bok choy and pull the leaves and stems apart. Blanch in boiling salted water for one minute, then drain and refresh in iced water and drain well again.
Heat a wok, then add the oil. When very hot, stir fry the bok choy and garlic for one minute. Add the salt, soy, oyster sauce and stock and cook for a further 30 seconds. Add the prosciutto, then toss through the bok choy and immediately remove from the heat.
Arrange bok choy and prosciutto on a plate. If the sauce is too runny, reduce for a moment over a high heat, then pour over the plate before pouring over the dish.