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1
Prepare a medium-hot fire in a charcoal grill with a cover, or preheat a gas grill to medium-high.
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2
Combine the mayonnaise and sun-dried tomatoes in a small bowl and mix well.
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3
Cover and refrigerate until ready to use.
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4
Place the oil in a 12-inch fire-proof skillet and set on the grill rack.
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5
When the oil is hot, add the onion, bell pepper, and mushrooms.
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6
Cook, stirring frequently, until tender, about 5 minutes.
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7
Add the spinach leaves and cook until the spinach is wilted, about 3 minutes.
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8
Transfer to a large bowl and add the sirloin, feta cheese, and salt.
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9
With your hands or a large spoon, gently mix well, handling the meat as little as possible to prevent compacting it.
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10
Form into 6 equal-sized patties.
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11
Pour the oil into the same skillet and place on the grill rack.
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12
When the oil is hot, add the prosciutto.
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13
Cook until well crisped, about 5 to 8 minutes.
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14
Transfer to a paper towel-lined plate to drain; set aside.
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15
When the grill is ready, brush the grill rack with vegetable oil.
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16
Place the patties on the rack, cover, and cook until the bottoms are brown, about 4 minutes.
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17
With a spatula, turn over the patties and cook an additional 4 minutes, or until done to your preference (internal temperature of 160 degrees F).
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18
During the last few minutes of grilling, top each patty with a slice of mozzarella cheese until melted.
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19
Lightly brush the cut sides of the rolls with the 4 tablespoons olive oil.
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20
Rub the cut sides of the garlic over the insides of the rolls, then sprinkle and press with the Parmesan.
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21
Place the rolls, cut sides down, on the outer edges of the grill rack to toast lightly.
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22
Spread the mayonnaise mixture on the insides of the warm toasted rolls.
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23
Layer the bottom rolls with divided greens, the patties, and divided frizzled prosciutto.
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24
Top with the remaining rolls, serve, and enjoy!
