With a sharp knife, make 20 slits across 1 side of the lamb and insert the garlic slivers. Place in a large non-reactive dish.
In a bowl, whisk together the oil, lemon juice, garlic, oregano, rosemary, salt, and pepper. Pour over the lamb and rub evenly across the surface. Cover with plastic wrap and marinate, refrigerated, for at least 2 and up to 6 hours, turning occasionally.
Remove from the refrigerator and let come to room temperature. Season lightly on all sides with Essence. Brush a grill lightly with olive oil and preheat to medium heat.
Remove the lamb from the marinade and place on the grill. Cook, turning occasionally until the meat reaches an internal temperature of 145 degrees F for medium-rare, about 1 1/2 hours. Remove from the grill and transfer to a platter. Tent with foil and let rest for 12 minutes before carving.
Thinly slice the lamb and place the meat in the center of the pita breads. Top with Tzatziki Sauce and chopped tomatoes, and serve.
Yield: 16 servings