Combine garlic, shallot, parsley, sage, and olive oil in small bowl. Following illustrations below, butterfly and pound flank steak into rough rectangle. With steak positioned so that grain runs parallel to edge of counter and opened side faces up, spread herb mixture evenly over surface of steak. Lay prosciutto evenly over steak, leaving 2-inch border along top edge. Cover prosciutto with even layer of cheese, leaving 2-inch border along top edge. Starting from bottom edge and rolling away from you, roll beef into tight log and place on cutting board seam-side down.

Starting ½ inch from end of rolled steak, evenly space 8 to twelve 14-inch pieces of butcher’s twine at 1-inch intervals underneath steak. Tie middle string first; then working from outermost strings toward center, tightly tie roll and turn tied steak 90 degrees so seam is facing you. Skewer beef directly through outermost flap of steak near seam through each piece of string, allowing skewer to extend ½ inch on opposite side. Using chef’s knife, slice roll between pieces of twine into 1-inch-thick pinwheels. Season pinwheels lightly with kosher salt and black pepper.

Turn all burners to high and heat with lid down until very hot, about 15 minutes. Scrape grate clean with grill brush. Dip wad of paper towels in oil; holding wad with tongs, wipe cooking grate. Leave primary burner on high and turn off other burner(s).

Grill pinwheels directly over hot side of grill until well browned, 3 to 6 minutes. Using tongs, flip pinwheels; grill until second side is well browned, 3 to 5 minutes longer. Transfer pinwheels to cooler side of grill, cover, and continue to cook until center of pinwheels registers 125 degrees on instant-read thermometer, 1 to 4 minutes (slightly thinner pinwheels may not need time on cooler side of grill). Transfer pinwheels to large plate, tent loosely with foil, and let rest 5 minutes. Remove and discard skewers and twine and serve immediately.