Heat the oil in a large deep skillet, saucepan or cast iron casserole. I use a cast iron casserole by Le Creuset.
Add the chopped onion and sauté for a minute or two.
Add the grated carrot, the basil, oregano and thyme and continue to sauté until the onion has softened.
Whisk the mustard into the chicken stock and add the stock to the pan. Bring to the boil.
Stir in the broken spaghetti.
Return the soup to the boil, stirring occasionally.
Reduce the heat, cover and simmer for about 8 minutes. The noodles should be almost tender, but not quite.
Add the chicken to the soup.
Whisk the flour into the milk.
Gradually whisk the milk into the soup, stirring as you go.
Simmer the soup, stirring occasionally, for about 3 to 5 minutes, until the soup has thickened slightly, the chicken is hot and the noodles are cooked.
Add salt and pepper to taste.