Heat the cooking oil in a wok or frying pan. Add the shallots (or onion), tomatoes, garlic and ginger. Saute for a minute. Season with fish sauce, soy sauce, pepper and sugar. Continue sautéing until softened and aromatic.
Add the mung bean sprouts and stir fry (high heat!) for about half a minute. Note that sprouts contain a lot of water and the water will get expelled when the sprouts touch the heat. So, the less time you cook the mung bean sprouts, the less water they will expel. Besides, you don’t really want to overcook the sprouts; you want them to retain a light crispness by the time the dish is done. So, stir fry for no more than a half a minute and keep the contents of the pan moving.
Add the chopped crispy pork belly. Stir fry for another half a minute just until the meat is heated through and the mung bean sprouts are done but still crisp.
Garnish with snipped greens before serving. A dipping sauce (fish sauce, soy sauce and crush chiles) is recommended.