Saute onions and garlic in oil until soft and golden. Add remaining ingredients and cook slowly for 10 minutes.
Spray a non stick cookie sheet with cooking spray. Spread tomato mixture over sheet in thin layer. Dry in a 140*F. oven, with the door open to first stop, for about 6 hours. Roll leather and store in a plastic bag.
May be frozen.
To reconstitute, add a volume of water that is 3 times the volume of leather. For leather that fills 1/2 cup, add 1 1/2 cups of water. Cook and stir over low heat until sauce is warm and smooth.