In a large pot, combine chicken broth, fresh lemon juice, shredded carrots, finely chopped onion, and finely chopped celery. Bring to a boil, then reduce to a simmer, cooking for 15-20 minutes.

In a separate bowl, mix margarine with all-purpose flour to create a smooth paste. Gradually whisk this into the soup, stirring continuously for 8-10 minutes until thickened.

Beat egg yolks in a small bowl. Slowly add hot soup to yolks while whisking vigorously. Return this mixture to the pot, stirring gently without boiling.

Stir in cooked white rice and diced cooked chicken. Cook on low heat, stirring occasionally for about 5 minutes until heated through.

Ladle soup into bowls; garnish with lemon slices. Serve with crusty bread.