Heat the large heavy-bottomed pot over medium heat and add a splash of oil. Once shimmering, add chopped onions, carrots, and celery. Cook, stirring occasionally, until the vegetables are tender and fragrant, about 5-7 minutes, and they begin to soften.
Add the minced garlic and freshly grated ginger to the pot. Sizzle for about 30 seconds until fragrant, with the mixture bubbling gently and filling the kitchen with a spicy aroma.
Pour in the chicken broth and add the bruised stalk of lemongrass. Bring the mixture to a gentle simmer, allowing the flavors to meld as the broth heats through.
Once simmering, stir in the shredded cooked chicken. Let the soup simmer uncovered for about 20 minutes, skimming any foam from the surface and stirring occasionally to prevent sticking.
Remove the lemongrass stalk and taste the broth, adjusting salt if needed. Squeeze in fresh lemon or lime juice to brighten the flavors and stir gently.
Ladle the hot soup into bowls, garnish generously with fresh herbs like cilantro or Thai basil, and serve immediately for a fragrant, comforting meal.
