DRAIN oranges, reserving liquid. Add enough water to reserved liquid to measure 1 cup; pour into medium saucepan. Bring to boil. Add couscous; cover. Remove from heat. Let stand 5 min.
MEANWHILE, combine spinach, chicken, vegetables and oranges in large bowl. Add dressing; toss to coat.
FLUFF couscous with fork. Add to salad; mix lightly. Serve warm or chilled.