Grecian Meatloaf Gyros

Name: Grecian Meatloaf Gyros
Ingredients: 1 egg, lightly beaten; 6 garlic cloves, minced; 3 tablespoons dried oregano; 1 1⁄2 teaspoons kosher salt; 1 teaspoon pepper; 1 lb ground lamb; 1 lb ground beef; 8 whole gyro-style pita bread (6 inches); 3 tablespoons olive oil, divided; 16 slices tomatoes; 8 slices sweet onions, halved; TZATZIKI SAUCE; 1 cup plain yogurt; 1 medium cucumber, peeled, seeded and chopped; 2 tablespoons lemon juice; 2 garlic cloves, minced; 1⁄2 teaspoon salt; 1⁄4 teaspoon pepper