Heat half the oil in a large non-stick skillet over medium heat. Add the cooked rice and crushed saffron. Cook, stirring constantly, for 3-4 minutes. Remove the rice from the skillet and set aside. Heat the remaining oil in the skillet and turn the heat to medium-high. Add the onion, celery, green pepper, red pepper, and garlic. Cook, stirring, for 2-3 minutes or until the vegetables are tender. Stir the tomato sauce, chili powder, sugar, salt, cayenne, and tomatoes into the skillet. Cook, stirring often, for 2 more minutes. Stir the rice back into the skillet. Cook, stirring, for 2 minutes or until mixed and heated through.