How to Make It
Heat grill or a grill pan to medium. Once it is hot, clean the grill grate with a wire brush. Just before grilling, oil the grill grate or grill pan.
Heat the oil in a large skillet over medium-high heat. Season the steak with ¼ teaspoon salt and ½ teaspoon pepper; cook 3 to 5 minutes per side for medium-rare. Let rest for 5 minutes, then thinly slice. Reserve the skillet.
Add the chard and garlic to the skillet and cook, tossing occasionally, until tender, 4 to 6 minutes.
Dividing evenly, fill the rolls with the chard, steak, and mozzarella. Grill, pressing down with a spatula, until the cheese is melted, 4 to 6 minutes per side. Serve with carrot sticks.