Heat the oil in a skillet and add the onions, celery, peppers, and garlic. Sauté until soft, about 5 minutes. Add the other ingredients, bring the mixture to a boil, cover and reduce the heat, and simmer for 15 minutes. You should be able to pick out the tomato skins as the mixture cools.
Ladle the salsa into two 1-cup freezer containers and let cool. You can keep the salsa in the freezer for at least 6 months. Thaw in the refrigerator before using.