Heat grill to medium-high. In a medium bowl, combine the tomatoes, bocconcini, basil, oil, and ¼ teaspoon each salt and pepper.
Grill the sausages, turning occasionally, until cooked through, 10 to 12 minutes. During the last 5 minutes of cooking, grill the rolls until slightly charred and crisp, 2 to 3 minutes.
Serve the sausages on grilled rolls and top with the tomato mixture.