Blanch whole tomatoes in boiling water for 2-4 minutes, until skins crack and are easy to remove.
Immediately transfer hot tomatoes into ice water, and let sit for 3-5 minutes. Peel tomatoes (skins should easily slip off), cut out cores, and chop to the desired size.
In a large non-reactive stock pot, combine chopped tomatoes, salsa mix, vinegar, onion, and bell pepper.
Bring to a boil; then reduce heat and simmer for 10 minutes, stirring occasionally.
Carefully transfer hot salsa to prepared canning jars.
Refrigerate and serve cold. Or can according to manufacturer recommendations.