In a large pot, combine the chicken thighs, garlic, ginger, scallion whites, kosher salt, black pepper, and water. Bring to a boil, then simmer uncovered for 15 minutes.

While the broth simmers, whisk together the black rice vinegar, soy sauce, and toasted sesame oil in a small bowl. Add crispy chili oil if desired.

After 15 minutes, remove the chicken, add noodles and carrots to the boiling broth, and cook for 3-4 minutes until tender.

While the noodles are cooking, shred the chicken into bite-sized pieces.

Return the shredded chicken to the pot, stir, and warm through for 1 minute. Adjust seasoning if needed.

Ladle soup into bowls, garnish with scallion greens, and drizzle the sauce over each bowl before serving.