Clean shrimp, remove shell and de vein. Cut into bite-sized pieces. Heat oil in large skillet. Saute green peppers and onions until soft but not browned. Stir in tomatoes and olives. Add oregano, garlic powder, saffron, salt and sugar. Simmer 20 30 minutes. Drain and halve artichoke hearts. Add to tomato mixture with shrimp. Cook 15 minutes longer. Blend cornstarch in water and add to tomato mixture, stirring until it thickens and boils. Serve at once with rice. Serves 4.