For the sauce: Pour the tomatoes into a 4- to 6-quart slow cooker and crush by hand. Stir in the tomato paste, olive oil, oregano, pepper flakes, garlic, bay leaves and 2 teaspoons salt.
For the meatballs: Place the onions, carrots, celery, parsley and garlic in a food processor and pulse to make a paste. Transfer to a large bowl and add the beef, pork, eggs, breadcrumbs, Parmesan and 1 teaspoon salt. Form into 1 ½-inch meatballs (you should get about 20 to 24) and nestle into the sauce in the slow cooker. Cover and cook on high for 4 to 5 hours or low for 7 to 8 hours. Discard the bay leaves before serving.
