Place the pork slab(s) in a wok, add about 1 cup of water to partially cover them. Bring it to a boil over medium-high heat. Cover, reduce to a simmer, and cook for about 15 minutes until slightly softened. Transfer to a plate, then thinly slice them once they have slightly cooled.
If the mushrooms are very dirty, quickly rinse and pat them dry. If they're clean, just wipe them with a damp cloth. Slice them into large, bite-sized pieces. Keep in mind that they will shrink as they cook.
Slice the chilies, remove the seeds and membranes, and rinse under cold water. To reduce heat from spicier varieties, blanch them in boiling water for about 3 minutes.
In a bowl, combine soy sauce, oyster sauce, Shaoxing wine, sugar, cornstarch, and 2 tablespoons of water. Mix until well combined, then set aside.
Spread the meat in the wok and brown it over medium heat. The pork will release liquid that evaporates, then the fat will start to render. Add a little oil if the meat sticks or needs more browning. Stir occasionally until the pork is evenly browned and slightly crispy. Season with salt and pepper, then transfer to a plate. Discard any excess rendered fat. Spread the mushrooms in the pan over medium-high heat. Let them sear for about 3 minutes without stirring too much to prevent them from becoming watery. Once they turn golden, flip them over. Sear the other side until golden brown. Then, transfer the mushrooms to a plate. Add a bit more oil to the pan and sauté the ginger until it's light golden brown. Then, add the onions and garlic and continue to sauté until they are soft and translucent.
Add the chili peppers to the pan and sauté for a few minutes to mellow their heat. Then, add the white parts of the scallions and cook until they are tender.
Return the pork and mushrooms to the pan. Pour the sauce over them, and toss everything together until the sauce thickens. If the sauce thickens too much or you prefer it thinner, add more water as needed, depending on the moisture released by the mushrooms during cooking.
Add the green parts of the scallions and season with ground pepper to taste. Toss them together, then turn off the heat.