Place the chicken thighs in a medium pot, add enough water to cover the chicken. Add the lemongrass, garlic, cilantro stems and roots, and green onions into the pot.
Bring to a boil, cover the pot with a lid and simmer for 20 minutes until the chicken is cooked. Salt & pepper to taste. Remove the chicken thighs and let them cool down before shredding them. You may save the poaching liquid for another recipe.
Mix the ingredients of the dressing in a small bowl and set aside.
In a small pot, boil the soaked glass noodles for about a minute until soft. Drain and rinse with cold water.
In a large mixing bowl, toss the cooked and cooled down glass noodles with mint leaves, cilantro leaves, cabbage, cucumber, carrots, shallots, and shredded chicken thighs. Pour in the dressing and mix thoroughly. Adjust seasoning to your taste.