Stir-fry bell pepper and celery in hot oil in a large skillet 2 to 3 minutes. Add garlic; stir-fry 1 minute.
Stir together cornstarch, ground red pepper, and soy sauce; add to vegetables, and stir-fry 2 minutes or until thickened.
Add mushrooms, water chestnuts, and green onions; stir-fry 2 minutes or until thoroughly heated. Serve over ramen noodles.