Add the two cans of whole peeled San Marzano tomatoes to the slow cooker. Use your hands to crush the tomatoes and release the juices. Then, add the minced onion, minced garlic, oregano, basil, salt, and pepper to the slow cooker.

Mix all of the ingredients in the slow cooker. Then, add the bay leaves.

Place the lid on the slow cooker and cook the sauce on high for 4 hours or on low for 8 hours. When the sauce is done, carefully remove the bay leaves and enjoy!