Pre-heat the grill or grill pan to high.
To butterfly the flank steak, start with the meat grain running up and down in front of you. With a knife, begin cutting the meat in half. Essentially, you want a thinner, larger flank steak. Continue cutting the flank steak in half until you reach about 1 inch from completely cutting through. Lay the cut flank steak open and even out the middle so there is not a thicker piece in the center. Or just ask the butcher to do this for you!
Spread the flank steak out so that the grain is running left to right. Layer the flank steak with salt and pepper, then the Asiago cheese, spinach, Gorgonzola cheese and scallions. Roll the flank steak tightly and away from you. Evenly insert the skewers 1-2 inches along the seam of the pinwheel to hold it together on the grill.
Next, make the pinwheels by cutting in between each skewer but not against the skewer; you want the same amount of meat on either side of each skewer. Grill the pinwheels on each side for about 3-4 minutes, or until your desired doneness.