Combine chicken broth, sliced lemongrass, and minced garlic in a large pot. Bring to a gentle simmer over medium heat, allowing the fragrant herbs to infuse the broth for about 10 minutes.
Remove the lemongrass pieces and add the boneless chicken pieces to the simmering broth. Cook until the chicken is cooked through and tender, about 8-10 minutes, stirring occasionally.
While the chicken cooks, pour boiling water over the rice noodles in a separate bowl. Let sit for 5 minutes until softened, then drain and set aside.
Add sliced carrots, soy sauce, and sesame oil to the pot with the chicken. Continue simmering for another 5 minutes, until the carrots are tender and flavors meld.
Stir the cooked noodles into the soup, ensuring they are heated through and coated with the flavorful broth. Taste and adjust seasoning with salt and pepper as needed.
Serve hot, garnished with sliced green onions for a fresh, crisp touch. Enjoy the aromatic, comforting bowl of chicken noodle soup.
