Cut and shred the cabbage, carrots, onions, tomatoes and cucumbers. See tips in post.
Place all the ingredients into a large pot and mix well.
Prepare syrup. In a medium pot, combine the oil, vinegar, sugar and canning salt. Bring the syrup to a soft boil and continue stirring until sugar dissolves.
Pour the syrup into the pot with all the veggies. Place on stovetop and cook the salad over med/high heat for 15-20 minutes. Mix the salad as it's cooking.
Meanwhile, prepare the jars.
When the salad is done cooking fill each jar with the salad.
Wipe any food from the rim of the jars. Close lid. Lightly twist on the band, NOT too tight. Add jars to water, cook 7 minutes. Remove jars from water. Tighten bands all the way.
Lay out a towel or small blanket on table or counter top, flip all jar. Cover jars with a towel or blanket and let it sit this way for about 12 hours or overnight.