Preheat the grill. Season the lamb and chicken with 2 tablespoons olive oil, salt and pepper. Brush the pita bread with the remaining olive oil. Place the lamb and chicken on the grill and cook for 2 minutes on each side. Place the pita bread on the grill and cook for 2 minutes on each side. In a mixing bowl, mix the yogurt, cucumbers, and lemon juice together. Season with salt and pepper. Spread the cucumber sauce evenly over each pita bread. Divide the lamb slices between the three pita breads. Divide the chicken up between the remaining pita breads. Garnish each sandwich with lettuce, onion and tomatoes. Place the pita bread on parchment paper. Roll the sandwich up tightly in the parchment paper, tucking the ends into the sandwich. With a serrated knife, slice the sandwiches in half and serve.