In a large bowl, combine the sesame oil, soy sauce, mirin (if using), minced garlic, and black pepper.
Add the thinly sliced pork belly to the marinade and mix well to coat evenly.
Let it marinate for at least 30 minutes, preferably longer for better flavor.
In a small bowl, combine the doenjang, gochujang, sesame oil, sesame seeds, honey or sugar, minced garlic, and chopped green onion.
Mix well until smooth and set aside.
Preheat a grill or grill pan over medium-high heat.
Grill the marinated pork belly slices for about 2-3 minutes on each side, or until they are nicely browned and cooked through.
Remove from the grill and cut into bite-sized pieces.
Arrange the grilled pork belly on a platter.
Enjoy your meal!