Spicy Pork Bulgogi

Name: Spicy Pork Bulgogi
Ingredients: 1 lb pork belly or 1 lb pork shoulder, thinly sliced; 1⁄2 medium onion, thinly sliced; 2 -3 green onions, roughly chopped; boston lettuce or romaine lettuce, leaves separated and washed; Marinade; 3 tablespoons gochujang korean red chili paste; 1 tablespoon korean red chili pepper flakes; 2 tablespoons soy sauce; 2 tablespoons rice wine or 2 tablespoons mirin; 2 tablespoons sugar; 1 tablespoon sesame oil; 1 tablespoon minced garlic; 1 tablespoon grated ginger; 1⁄8 teaspoon ground black pepper