Bring water & salt to boil in a large saucepan. Remove from heat & stir in couscous; cover & let stand 5 minutes. Fluff couscous with a fork.
Combine olive oil & lemon juice. Add oil mixture to couscous, stirring to coat. Let stand until completely cooled.
Stir in spinach, green onions & chopped dill. Cover & refrigerate until ready to serve (up to 12 hours). Add feta cheese & stir just before serving.
Serves 6-8