Heat the vegetable oil in a wok, add sliced onions and diced tofu and stir-fry it on high heat for around 2-3 minutes.
Add the garlic, ginger and stir-fry for a further 1-2 minutes. Then add the pak choi leaves (whole or sliced as you please) and soy sauce. Fry for another minute or so, until the greens have started to wilt slightly.
Remove the wok from the heat, garnish with sesame oil and sesame seeds. Serve the pak choi immediately with the rice and a chilli-garlic oil for some heat.