In a large bowl combine tomatoes, bread crumbs, onion, zucchini, roasted peppers, egg product, half of the parsley, the garlic, and black pepper. Add ground beef and ground lamb; mix well.
Coat a 3 ½- or 4-quart slow cooker with cooking spray. Cut three double-thick, 18x3-inch heavy foil strips. Crisscross strips in the prepared cooker; coat strips with cooking spray. Place meat mixture on top of strips in cooker; pat into an oval or round loaf. Cover and cook on low-heat setting for 3 ½ hours or on high-heat setting for 1 ½ hours.
If using low-heat setting, turn to high-heat setting. In a small bowl combine ketchup, Worcestershire sauce, mustard, and vinegar. Spoon ketchup mixture over meatloaf. Cover and cook for 30 to 45 minutes more or until an instant-read thermometer registers 165°F.*
Using the foil strips, carefully lift meatloaf from cooker, allowing liquid to drip off. Place on a serving plate. Remove foil strips. Sprinkle meatloaf with cheese (if desired) and the remaining parsley. Cover and let stand for 15 minutes before serving.