Preheat oven to 375 degrees. Line a small rimmed baking sheet with foil or parchment paper and set aside.
Add the onion, celery and garlic to the bowl of a food processor and pulse 10 – 15 times or until finely chopped. Add to a large bowl along with the ground beef, veal, and pork, egg, bread crumbs, 1 teaspoon salt, cayenne, and allspice. Gently but thoroughly mix the meats and other ingredients. Do not over mix or the meatballs will be tough. Use a ¼ cup measure and form the meat into about 15 meatballs. Place on the prepared baking sheet and bake for 25 – 30 minutes. Remove from oven and cover with foil to keep warm.
Meanwhile, in a large sauté pan over medium heat, combine the tomato sauce, tomato paste, red wine vinegar, honey, Worcestershire sauce, 2 teaspoons salt and, a pinch of cayenne. Bring the mixture to a boil then turn the heat to low and simmer uncovered for 10 – 15 minutes stirring occasionally.
In a large bowl, whisk the olive oil, apple cider vinegar, honey, salt and pepper. Add the cabbage and apple and toss to coat. Set aside.
Add the cooked meatballs to the sauce and simmer for an additional 10 minutes. Serve 3 meatballs in each roll and top with the Poppy Seed Cole Slaw.