Pour the broth into a heavy large saucepan
. Cover the pan and bring the broth to a boil over high heat. Stir in the orzo. Cover partially and cook until the orzo is tender but still firm to the bite, stirring frequently, about 7 minutes. Drain
the orzo through a strainer
. Transfer the orzo to a large wide bowl and toss until the orzo cools slightly. Set aside to cool completely.
Toss the orzo with the beans, tomatoes, onion
, mint, and enough vinaigrette to coat. Season the salad, to taste, with salt and pepper, and serve at room temperature.