Pour 1 cup of hot water over couscous, stir in lemon zest, cover and let set 10 minutes. Fluff with a fork and set aside.
Heat 1 tbsp oil and sauté leeks until tender, about 5 minutes.
Remove leeks from pan, add remaining 1 tbsp oil to pan and Vidalia onion, cooking until lightly caramelized, about 15 minutes.
Stir cooled leeks and onions into couscous, stir in chives, season and chill until ready to serve.