Place the tomatoes green peppers onions and grease in a saucepan and cook until tender
While they are cooking mix together the cornstarch and sugar with a cup of water
When the tomato mixture is done and the rest of your meal is ready bring the tomatoes to a boil and pour the cornstarch mixture into the tomatoes stirring constantly
Turn off and let set to thicken for a few minutes
Best when served over fried potatoes or as a sauce over hamburgers salmon cakes or other meat