Heat the oil in a pan and fry the white leek and onion and carrot for 5-6 minutes, until softened. Add the chicken, stock and 1/2 the lemon. Bring to the boil then simmer for 10 minutes.
Add the green leek and orzo and simmer for a further 5 minutes until the chicken is cooked through and no pink meat remains and the orzo is al dente.
Remove the lemon and discard. Season the soup to taste and shred the chicken
using 2 forks. Cut the remaining lemon into 4 wedges and serve with the soup,
to squeeze over.