Grilled Meatloaf Sandwiches

Name: Grilled Meatloaf Sandwiches
Ingredients: 1 cup whole milk; 3 potato rolls, torn; 1 tablespoon chopped fresh rosemary; 4 celery stalks, chopped; 2 carrots, chopped; 1 white onion, chopped; 1 pound ground bison; 1 pound lean (90/10) ground pork; 1 pound ground veal; 1 cup grated Parmesan cheese; 1/4 cup Worcestershire; 3 eggs, lightly beaten; Freshly ground black pepper; 1 cup ketchup; 1/2 cup dark brown sugar; 2 tablespoons Dijon mustard; 1 tablespoon apple cider vinegar; Canola oil spray, for spraying meat and rolls; 12 to 15 onion slider rolls; 12 to 15 slices Cheddar cheese; 1/2 cup mayonnaise; 12 to 15 pieces green leaf lettuce; 12 to 15 thinly sliced pieces red onion; 12 to 15 slices tomato