Melt butter in medium saucepan on medium heat. Add onion; cook and stir 2 minutes or until softened. Add lemon zest and bay leaves; cook and stir 30 seconds. Add water and salt. Bring to boil.
Stir in couscous. Cover. Remove from heat. Let stand 5 minutes or until all of the water is absorbed. Remove bay leaves. Drizzle with lemon juice. Fluff couscous with fork before serving.