FOR each serving: Grill 1 beef patty on medium-high heat 2 to 3 min. on each side or to medium (160ºF), or desired doneness. Top with 2 cheese slices. Grill 30 sec. or until cheese begins to melt.
SPREAD 1/2 Tbsp. of the steak sauce onto bottom half of roll. Top with 1/2 cup spinach, cheeseburger, 2 prosciutto slices, 1 Tbsp. onions and 1 Tbsp. of the remaining steak sauce. Cover with top of roll.