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1
Place the mayonnaise and harissa in a medium bowl and mix to incorporate.
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2
If not using immediately, cover and refrigerate for up to 1 day.
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3
Place all of the ingredients except the oil in a large bowl and, using your hands, mix until just combined.
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4
Divide the meat into 4 equal portions.
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5
Shape each portion into an even 1/2-inch-thick patty that is about 1 inch wider in diameter than the kaiser rolls.
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6
Using your thumb, make a shallow 1-1/2-inch-wide indentation in the center of each patty (this helps the burgers cook more evenly).
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7
Transfer the patties to a plate and refrigerate while you prepare the grill.
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8
Heat a grill pan or outdoor grill to medium high (about 450 degrees F to 550 degrees F).
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9
When the grill is ready, use tongs to rub the grate with several layers of paper towels dipped in vegetable oil.
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10
Place the patties on the grill indentation-side up, close the grill, and cook undisturbed ( press down on the patties) until grill marks appear on the bottom, about 6 minutes.
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11
Using a spatula, flip the patties, close the grill, and cook until the juices run clear and the patties are firm to the touch, about 6 minutes more.
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12
Remove to a clean plate and let rest in a warm place or tent loosely with foil for 5 minutes.
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13
Spread about 1 tablespoon of the harissa mayonnaise on each top and bottom roll (2 tablespoons per burgeryou will have some mayo leftover).
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14
Divide the feta among the bottom halves and top the feta with 4 cucumber slices per burger.
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15
Place a lamb patty on each bottom half and top with a lettuce leaf.
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16
Close with the roll tops and serve immediately.
