This is sometimes called "Chinese" vegetable stew in Thailand, because the chosen vegetables are usually of Chinese origin. You can make substitutions, and some recipes for this stew call for as many as 10 different vegetables. You do need at least 4 to get the variety of tastes and textures required, but if the produce market yields more on the day, then you can indeed use more (keep the overall quantity about the same). Though called a vegetable stew, this is by no means a *vegetarian* dish. It contains a substantial amount of meat. The essential flavor of the dish comes from the belly pork. If you prefer you can use a pound of belly pork and omit the poultry, but you shouldn't omit the pork altogether.
This is a "one plate" meal - a single dish forming the entire meal (as opposed to the more usual dining style in Thailand with several contrasting dishes).
For 4 Person(s)
Bring the stock to a boil and add the pork, poultry, fish sauce, soy sauce, and Maggi sauce. Boil uncovered until the meats are just cooked. Add the vegetables, tofu, and noodles. In a wok heat some oil, and fry the soybean paste until fragrant. Saute the garlic and ginger. Add the soybean paste, garlic and ginger to the soup. Taste, and adjust the fish sauce and pepper to suit your preference.
Remove from the heat and serve when the vegetables are done.