Butterfly steak by slicing it horizontally with a very sharp knife, stopping about 1 inch before you would slice all the way through (or ask your butcher to butterfly it for you). 

To grill, soak 8 toothpicks in water for at least 20 minutes and prepare the grill for medium heat cooking. 

Secure rolled steak at seam and ends with toothpicks. 

Brush outside of steak with oil and grill, turning frequently, until steak is deeply browned all over and cooked to your desired doneness, 15 to 20 minutes for medium-rare (an instant-read thermometer inserted into the center should register 130°F). 

Transfer steak to a cutting board, cover loosely with foil and let stand 10 minutes. 

Remove toothpicks and thinly slice.

To pan-sear steak, cut rolled steak into 8 slices and secure each piece with a toothpick at the side (these toothpicks need not be soaked in water). 

Heat oil in a large skillet over medium-high-heat. 

Add steak slices and cook, turning slices once, until well browned and meat is cooked until medium-rare to medium throughout, 6 to 7 minutes per side. (Don't worry if some of the cheese melts out.) 

Remove toothpicks and serve.