Traditional Gyros

Name: Traditional Gyros
Ingredients: 1 small onion, cut into chunks; 1 pound ground lamb; 1 pound ground beef; 1 tablespoon minced garlic; 1 teaspoon dried oregano; 1 teaspoon ground cumin; 1 teaspoon dried marjoram; 1 teaspoon dried thyme; 1 teaspoon dried rosemary; 1 teaspoon freshly ground black pepper; 0.25 teaspoon sea salt; 12 tablespoons hummus; 12 pita bread rounds; 1 small head lettuce, shredded; 1 large tomato, sliced; 1 large red onion, sliced; 6 ounces crumbled feta cheese; 24 tablespoons tzatziki sauce