In a medium-sized mixing bowl combine 1 pound ground beef, 3 ounces sliced pancetta,1 teaspoon minced garlic, ¼ teaspoon salt, ¼ teaspoon pepper, and 2 tablespoons prepared pesto. Mix well then divide and shape the meat mixture into four patties.
In a small bowl combine ¼ cup mayonnaise and the remaining 2 tablespoons pesto. Chill until ready to use.
Heat the grill to medium-high heat. Grill burgers for about 5-7 minutes on each side or until a thermometer reads 160 degrees Fahrenheit.
Top each burger with a slice of mozzarella cheese and grill until the cheese is melted.
Spread the pesto mayonnaise on 4 Italian rolls and top with sliced red onion, tomato, and arugula.