1. Place all of the ingredients except the lemon juice in a 4-quart pot. Cover and bring to a boil over high heat. Reduce the heat to low, cover, and simmer, stirring occasionally, for 30 minutes, or until the vegetables are tender and the orzo is cooked al dente.
2. Remove the chicken breast from the soup and cut into strips. Then return to the pot. Add the lemon juice, stirring well to mix. Remove and discard the bay leaf.
3. Ladle the hot soup into individual bowls and serve immediately.