In a bowl, whisk together the doenjang, gochujang, grated garlic, grated ginger, sesame seeds, pineapple juice, mirin, soy sauce, and sesame oil. Reserve a small portion of the marinade for dipping sauce. Add the pork belly strips to the remaining marinade and mix well to coat. Cover and refrigerate for at least 2 hours or overnight for more flavour.
Heat a griddle pan or BBQ over high heat. Cook the marinated pork belly in batches, allowing it to caramelise and develop a golden-brown crust. Flip and cook until slightly charred and cooked through.
Soak the thinly sliced spring onions in ice water for a couple of minutes to make them crisp. Drain well. In a small bowl, mix white vinegar, gochugaru, sugar, soy sauce, and sesame oil. Add the drained spring onions and toss to coat.
Place fresh lettuce leaves on a plate. Cut the cooked pork belly into bite-sized pieces. Serve with the chilli flake spring onions and the reserved dipping sauce.
