In a large bowl, combine ground lamb, ground beef, chopped onion, minced garlic, oregano, marjoram, rosemary, cumin, salt, paprika, bread crumbs, and pepper
Transfer the meat mixture into a loaf pan and press down to compact it. Bake in a preheated oven at 325°F for 60 minutes or until fully cooked.
Remove from oven and let rest for 10 minutes. Slice the meat into thin strips.
Warm pita breads. Spread tzatziki sauce on each pita, add slices of gyro meat, and top with tomato, red onion, and lettuce. Fold and serve.