In a bowl, combine ground lamb, ground beef, fresh bread crumbs, minced onion, garlic, allspice, coriander, and cumin.

Add 1 teaspoon of salt and 1/8 teaspoon of black pepper and mix well.

Form the mixture into 4 patties, cover, and chill for 2 hours.

In another bowl, whisk together red wine vinegar, dried oregano, 1/4 teaspoon salt, and 1/8 teaspoon pepper.

Gradually whisk in the olive oil until well blended.

Add chopped tomatoes, sliced onions, and cucumbers and stir to coat.

Cover and let marinate for at least 2 hours, but no more than 8 hours.

When ready to cook, oil and preheat your grill.

Grill the patties as you would hamburgers for 10-15 minutes, or until no pink remains but the burger is still moist.

Once the burgers are fully cooked, slit pita pockets open on the sides to form open pockets.

Warm the pita up by setting it briefly on the side of the grill.

Place a burger inside each pita pocket.

Serve with bowls of the tomato topping, shredded lettuce, and tzatziki sauce on the side for guests to add as desired.