Preheat oven to 450 degrees with rack in center. Between two sheets of plastic wrap, pound steak to 1/2-inch thickness with a meat mallet or heavy skillet. Using a sharp knife, score the steak on one side in a cross-hatched pattern. In a large bowl, whisk together oil, vinegar, and garlic. Marinate at least 20 minutes or up to overnight.

Remove steak from marinade. Lay steak on cutting board, scored side down, with a short end facing edge of work surface. Cover steak with cheese, scallions, and peppers, leaving 1/2-inch border on the long sides and 2-inch border at the far short end. Season with salt and pepper. Starting from closest side, roll up tightly. Using kitchen twine, tie steak crosswise. Season with salt and pepper.

Place, seam side down in a baking dish or on a rimmed baking sheet, and roast until juices run clear, 35 to 40 minutes for medium rare. Let rest 10 minutes, and remove string before slicing.