Gyro Burger

Ingredients

• 1 cup plain Greek yogurt
• 1/4 cup crumbled reduced-fat feta cheese
• 1/2 cup chopped peeled seedless cucumber
• 1/8 teaspoon salt
• 1/8 teaspoon black pepper
• 1 1/4 pounds ground lamb
• 2 teaspoons Greek seasoning (such as McCormick)
• 6 whole-grain pita breads
• 6 large Boston lettuce leaves
• 2 medium tomatoes, thinly sliced
• 1/2 red onion, peeled and thinly sliced