- Put the lamb in a bowl and add the garlic, cloves, cumin, and plenty of freshly ground black pepper. Mix with your hands until well combined, then shape into four burgers. Chill until ready to cook.
- Mix the red onion with the vinegar and sugar. Let marinate while you prepare the sauce. Squeeze the cucumber to remove excess moisture, then mix with the yogurt, garlic, mint, and a little salt and pepper. Chill.
- When ready to eat, heat a ridged cast-iron grill pan. Sprinkle the burgers with a little kosher salt and brush with olive oil. Cook the burgers until browned and cooked through, 3-4 minutes on each side.
- Meanwhile, split the rolls and toast them. When the burgers are cooked, assemble your creation with baby spinach leaves, tzatziki sauce, and the drained marinated onions.