Fill a medium saucepan with water. Add the bay leaves, smashed garlic and zest. Salt the water generously and bring it to a boil over medium-high heat. When boiling, add the couscous. Cook until cooked through, 7 to 8 minutes, and then drain. Discard the bay leaves, garlic and zest.
Meanwhile, in a large bowl, toss together the chopped garlic, cranberries, vinegar, scallion whites and celery. Season with salt and let sit for 20 minutes to soften.
Stir in the couscous, parsley and scallion greens. Drizzle with oil. Taste and re-season. Serve warm or at room temperature.