Preheat the broiler.
In a small bowl, combine the cheese and butter.
In a medium bowl, combine the meat with the sage, garlic and lemon zest; season with salt and pepper and form into 4 patties. Drizzle the patties with EVOO. On a griddle pan or in a large skillet, cook the patties over medium- high heat, turning occasionally, 10 to 12 minutes. Transfer the burgers to a plate. Add the prosciutto to the skillet; cook until crisp on both sides, turning once, 2 minutes. Transfer the prosciutto to a plate.
Toast the rolls under the broiler. Slather with theGorgonzola butter while hot.
In the same skillet, wilt the spinach, if using, over medium-high heat and place some on each roll bottom. Top with the patties, prosciutto and roll tops.