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, basil, mint, and enough vinaigrette to coat. Season the salad, to taste, with salt and pepper, and serve at room temperature.
Mix the vinegar, lemon juice, honey, salt, and pepper in a blender. With the machine running, gradually blend in the oil. Season the vinaigrette, to taste, with more salt and pepper, if desired.