Slice pork tenderloin into bite-sized strips or cubes. Set aside for later in the recipe. Also, set aside 1/4 cup of chicken broth for later.
Add the rest of the chicken stock to a large dutch oven, along with mushrooms, vinegar, soy sauce, ginger, and garlic chili sauce. Whisk to combine. Heat over medium-high heat to bring broth to a simmer.
While waiting for the soup to simmer, whisk cornstarch and 1/4 cup of chicken broth that you set aside to make a slurry. Once the soup is simmering, stir in the slurry for 1 minute to help thicken the soup.
While stirring the soup in a circle, slowly drizzle the whisked egg into the center of the swirling soup. Once the egg hits the hot soup, they will turn into egg ribbons. Add in the pork, green onions, and sesame oil. Finish the soup off with salt and pepper, to taste. If you want more heat, add in some more chili garlic sauce. Serve immediately.