Mediterranean Kebab Salad

Name: Mediterranean Kebab Salad
Ingredients: ½ cup plain Greek yogurt; 1 cup crumbled feta cheese; 2 teaspoons chopped fresh dill; 1 tablespoon red wine vinegar; ½ teaspoon Worcestershire sauce; ½ teaspoon garlic powder; ¼ teaspoon onion powder; ¼ teaspoon salt; ½ teaspoon freshly ground black pepper; 1 tablespoon whole milk (plus more as needed); 1 medium yellow onion (quartered); 4 garlic cloves; 2 cups packed parsley leaves; 1 pound ground beef; 1 pound ground pork; 1 teaspoon freshly ground black pepper; 1 teaspoon salt; ½ teaspoon ground allspice; ½ teaspoon cayenne pepper; 1 teaspoon cumin; ½ teaspoon ground sumac; ½ teaspoon ground nutmeg; ½ teaspoon smoked paprika; 2 4-ounce packages of salad greens