Cut onions, tomatoes, and bell peppers into two-inch cubes. Shred the carrots on the largest side of a cheese grater.
Gather and measure the oil, vinegar, salt, sugar, and peppercorns.
In a large pot, preheat oil and add in the onions. Sauté over medium-heat for about 3 minutes, or until the onion turns translucent and softens.
Add the shredded carrots and sauté for another 3 minutes.
Add bell peppers and sauté for another 3 minutes.
Add the diced tomatoes, followed by the salt, sugar, vinegar, and black peppercorns. Let simmer for about 15 minutes, stirring occasionally.
Now it's time to sterilize the jars for canning. Preheat the oven to 215°F. Using hot water and antibacterial soap, wash the jars and lids thoroughly. Place them directly on the oven racks for about 15 minutes, or until they are completely dry. Fill the jars with the salad while it's still hot. Using a kitchen towel to protect your hands, close the lids as tightly as possible and turn the jars upside down. Cover them with a towel and let them sit for 4-5 hours to complete the sealing process.
Store canned salad in a cool place for 3 - 6 months. For best results, let them marinate for a couple of weeks before opening. Enjoy on toasted bread or smothered over your favorite protein!