Preheat a gas or charcoal grill to a medium-high temperature (about 400°F).
Place the ground beef, garlic, gorgonzola cheese, sun-dried tomatoes, balsamic vinegar, parsley, salt and pepper in a large bowl. Using your hands, combine the ingredients gently and form into 4 equally sized patties. Chill for 15 minutes.
Oil the grill grates, add the burgers and cook until you see juices start to accumulate on the top of the patties, approximately 4 minutes. Carefully flip the bugers and continue grilling for 2 minutes. Top each burger with a slice of fontina and grill until cooked to your liking, 1 to 2 minutes more. Transfer to a plate and allow to rest for 5 minutes.
Place a slice of tomato on the bottom half of each roll. Season with a little salt and pepper, then add a burger and top with a slice of prosciutto. Serve immediately.