
1 tablespoon olive oil
1½ pounds boneless beef top sirloin steak, cut into thin strips
1 medium green bell pepper, seeded and cut into julienne strips
1 medium red bell pepper, seeded and cut into julienne strips
Salt and ground black pepper, to taste
Salted butter, softened
12 (½-inch-thick) slices French baguette
6 slices provolone cheese, cut in half