Place the meat in a non-reactive bowl. Mix together the lemon juice, oil, salt, pepper, 1 tablespoon oregano, garlic, and grated onion, and pour over the meat. Cover and chill at least 2 hours and up to overnight. Thread the meat onto metal or bamboo skewers.
Heat the oil on a griddle or in a large skillet over high heat. Add the onions, remaining teaspoon oregano and Essence to the griddle and cook light brown, about 6 minutes, stirring occasionally. Remove from the pan.
Preheat a grill. Grill the skewers, turning occasionally, until brown on all sides. Remove from the grill. Quickly heat the pita bread on the grill until just warmed through and pliant. Holding a pita in the left hand, and the skewer in the right hand, pull the contents from the skewer into the pita bread. Repeat with the remaining skewers. Divide the cooked onions among the pita, and top with Tzatziki (cucumber sauce). Serve immediately.
Yield: 4 to 6 servings