Chicken and Pork Souvlaki

Name: Chicken and Pork Souvlaki
Ingredients: 1 cup olive oil; 1/2 cup full-fat Greek yogurt; 1/4 cup fresh lemon juice; 1 teaspoon ground cumin; 1 teaspoon dried oregano; 1 teaspoon kosher salt; 1/2 teaspoon Aleppo pepper; 1/2 teaspoon freshly ground black pepper; 2 cloves garlic, finely grated; 1 pound boneless, skinless chicken breast, cut into 1-inch pieces; 1 pound pork tenderloin, cut into 1-inch pieces; 2 red onions, each sliced into 3 thick slices; 2 lemons, sliced in half; Olive oil, for drizzling; Kosher salt and freshly ground black pepper; Chopped romaine lettuce, pita and tzatziki, for serving