In slow cooker sauté together the onion, garlic, green pepper, and vegetable oil. Cook until onion is transparent. Add chopped tomatoes, oregano, basil, parsley, sugar, salt, and ground black pepper. Cook for 2 to 3 hours on low heat. Stir frequently. Let sauce cool. Pour sauce into quart size freezer containers. Store in freezer. When ready to use sauce, stir in tomato paste.
This is a great sauce to make and freeze when you have a surplus of tomatoes from your garden. Beef lovers can add in a half pound of ground chuck for a ?meatier? sauce. Makes 3 quarts.