In a pot, bring chicken, broth, rice, half of ginger, scallion white and light-green parts, 1 1/2 teaspoons salt, and 4 cups water to a boil. Reduce heat to medium-low; partially cover and simmer, stirring a few times, until chicken is just cooked through, about 20 minutes. Transfer chicken to a plate.Advertisement
Increase heat to medium and stir in mushrooms; boil, uncovered, until rice breaks down and mixture is creamy, about 20 minutes. Meanwhile, remove and discard skin and bones from chicken; shred meat into bite-size pieces. Remove ginger and scallions from congee; discard.
Thinly slice scallion tops; thinly slice remaining half of ginger into matchstick-size pieces. Stir chicken meat and any accumulated juices into congee and serve topped with scallion tops, ginger, sesame oil, and chili sauce.
Use short-grain rice, such as arborio, for a creamier porridge. Long-grain rice, like basmati or jasmine, yields a thinner texture.