Coat a large Dutch oven with cooking spray; add margarine. Place over medium-high heat until margarine melts. Add onion, celery, 3/4 cup green pepper, and garlic; saute until tender.
Stir in dry mustard and next 7 ingredients; cook 2 minutes, stirring occasionally. Stir in tomato; cook over medium heat 10 minutes, stirring occasionally. Add broth; bring to a boil. Add remaining 3/4 cup green pepper, chicken, rice, and green onions; stir well. Bring to a boil; cover, reduce heat, and simmer 20 minutes or until rice is tender.