Heat the oil in a large sauce pan over a medium heat. Add the onion, garlic, celery, carrots, a little salt and lots of black pepper. Cook for about 10 minutes, stirring gently. You just want the vegetables to soften, not brown. Stir through the chicken and cook for another five minutes.
Stir in the stock and bring to a boil. Cover and simmer for 10 minute. Then add the noodles and thyme leaves and cook for another 10 minutes. Stir through the Worchestershire sauce, taste and season.
Divide into four bowls, sprinkle over the scallions and serve.