Method:
1. Heat oil in a frying pan over medium-high heat. Add chicken and garlic and cook  for 3 minutes or until cooked through.
2. Bring stock to the boil in a medium saucepan, reduce heat to low and simmer. Add the chicken mixture. Whisk the egg white until frothy, add to the soup in a thin steady stream, whisking the soup continuously.
3. Stir in the lemon rind, juice and herbs. Ladle soup into bowls. Serve with Greek yoghurt and chives.