Cook couscous as directed on package, using water, oil and 1/2 teaspoon salt.
Meanwhile, melt margarine in large skillet over medium-high heat. Sprinkle chicken with 1/4 teaspoon salt and pepper; add to skillet. Cook 8 to 10 minutes or until chicken is fork-tender and juices run clear, turning once. Remove chicken from skillet; cover to keep warm.
In same skillet, cook onion 2 to 3 minutes or until tender. Add orange juice and broth; bring to a boil. Reduce heat. Add marmalade and chicken; simmer 3 minutes. Serve chicken with onion mixture over couscous. If desired, garnish with fresh orange slices.