Add the chicken and onion, then simmer for 3 minutes.
Add the carrots, celery, thyme, salt & pepper.
Cook until the carrots are tender, yet crunchy.
Add the noodles and cook until they are warmed. See notes.
Season with salt and pepper to taste.
Notes
I always add cooked noodles to my soup, because dried noodles will soak up your soup broth. Just boil your noodles ahead of time and set them aside until you are ready to add them.