Gather all your ingredients, preparing the aromatics by bruising the lemongrass and slicing the ginger to release their fragrant oils.
Place the large pot over medium heat and add a splash of oil if desired. Toss in the lemongrass and ginger slices, sautéing for about 2-3 minutes until they become fragrant and slightly toasted, filling your kitchen with a citrusy, spicy aroma.
Pour in the chicken stock and add the lime leaves along with the fish sauce. Bring the mixture to a gentle simmer, allowing the flavors to meld over the next 20 minutes. Keep the heat steady so the broth stays clear and fragrant.
After simmering, remove and discard the lemongrass and lime leaves. Stir in the shredded chicken and sliced mushrooms, then cook for another 5 minutes until the mushrooms are tender and heated through.
Finish by squeezing in fresh lime juice and tasting the broth. Adjust seasoning with more fish sauce or lime if needed to balance the flavors.
Ladle the hot soup into bowls, garnishing each with sliced chili and chopped cilantro for a burst of color and fresh flavor right before serving.
Serve immediately while steaming hot, enjoying the vibrant, fragrant layers of this comforting Thai chicken soup.