1. Cook asparagus and snow peas in large pot of boiling salted water 2 to 3 minutes, or until crisp-tender.
2. Drain, and rinse under cold water.
3. Bring broth and lemon zest to a boil in large pot. Put couscous in bowl, and stir in broth. Cover, and let stand 10 minutes. Discard lemon zest.
4. Fluff couscous with fork, and stir in asparagus, snow peas, radishes, lemon juice, chives, parsley, and mint. Season with salt and pepper.