Shred the cooked chicken into bite-sized pieces and set aside.
Slice the fennel bulb thinly, about 1/8-inch thick, revealing its crisp, slightly licorice-like texture.
Prepare the lemongrass stalks by brushing off any dirt, bruising the lower bulb to release flavor, and doubling the stalks for easy removal later.
In a large soup pot, heat the olive oil over medium heat. Add the minced garlic and cook for about 30 seconds until fragrant, listening for a gentle sizzling and smelling the aroma.
Add the sliced fennel and cook for 3-4 minutes, stirring occasionally, until it begins to soften and turns slightly translucent with a subtle aroma of anise.
Pour in the chicken broth, then add the bruised lemongrass stalks. Bring the mixture to a gentle simmer, allowing the flavors to meld for about 10 minutes.
Remove the lemongrass stalks from the broth, discarding them, and season the broth with salt and pepper to taste.
Add the shredded chicken pieces to the broth, letting them warm through for about 2 minutes.
Stir in the cooked noodles, allowing them to absorb some of the broth’s fragrant flavors and heat up for 2-3 minutes.
Taste the soup and adjust seasoning if needed, perhaps adding a pinch of salt or pepper for balance.
Serve the soup hot in bowls, garnished with fresh fennel fronds or herbs if desired, enjoying the aromatic, colorful broth.
