Bring broth to a boil in a large saucepan; add beans, and return to a boil. Cover, reduce heat, and simmer 20 minutes or until tender. Drain beans, reserving 1 cup broth in pan, and keep warm.
Whisk together yogurt and cornstarch; whisk into broth. Bring to a boil over medium heat, stirring constantly. Boil, stirring constantly, 1 minute or until thickened. Stir in beans, lemon juice, and remaining ingredients. Garnish, if desired.