1. Place chayote, carrot, corn, jicama, and apple in a large stockpot, and then add the water, rock sugar, and salt. Bring to a boil, and then reduce the heat to medium-low and simmer, uncovered, until vegetables are sweet to the taste (about 1 hour).
2. Heat ¼ cup (60 ml) of the oil in a medium skillet over low heat. When hot, add minced lemongrass, garlic, leek, chili pepper, bruised lemongrass stalks, chili flakes, sugar, and stock powder. Cook and stir until slightly golden (about 3 minutes). Remove from heat.
3. Using tongs or chopsticks, transfer lemongrass stalks to the large pot of vegetables. Reserve half of the cooked mixture in a small bowl to serve as a condiment with each bowl of soup.
4. Add the mock beef slices and mushrooms to the remaining half of mixture in the skillet and cook and stir over medium-low heat until tender (2 to 3 minutes). Add tofu cubes, stir gently, and then remove from heat and set aside.
5. Heat the remaining ¼ cup (60 ml) oil in a small skillet over medium-low heat. When hot, add the tofu and cook until golden brown on all sides (10 to 15 minutes). Transfer to a cooling rack or paper towel–lined plate to drain, and then cut into bite-size pieces.
6. If using store-bought rice vermicelli noodles, follow the directions on the package (page 00). If using fresh, quickly blanch them in hot water to warm.
7. Fill one-third of each serving bowl with rice vermicelli noodles, and then top with mushrooms, tofu, and mock beef slices. Ladle hot broth over the top and garnish with chopped cilantro.
8. Serve with a platter of lettuce, herbs, bean sprouts, banana blossom, and lime wedges, along with the reserved condiment mixture.

Recipe reprinted with permission from Quarto Publishing Group USA Inc.