Saute onions and celery in shortening until tender, but not brown. Add tomatoes, tomato sauce, salt, sugar, Worcestershire sauce, chili powder and Tabasco sauce. Simmer 45 minutes, uncovered. Mix cornstarch and water. Stir into sauce and cook until mixture thickens and bubbles. Add shrimp and green pepper. Cover and simmer 5 more minutes. Serve over rice.