In a bowl, stir together the couscous, garlic, lemon zest, scallions, a pinch of salt and a grind or 2 of pepper. In a pot on high heat, bring the chicken stock and butter to a boil. Immediately pour over the couscous mixture, then quickly cover tightly with a lid or plastic wrap. Let sit for 5 minutes. Add the mint, fluff with a fork and stir in the olive oil. Serve warm.