In a large bowl, whisk together the sesame oil, soy sauce, light corn syrup, grated ginger, minced garlic, mirin, gochugaru, salt, and black pepper to make the marinade.
Add the sliced chicken thighs to the bowl and toss until every piece is evenly coated with the marinade.
Cover the bowl and refrigerate for 2 hours to marinate.
Preheat a grill or grill pan over medium-high heat and brush the surface lightly with oil to prevent sticking.
Grill the marinated chicken until golden brown and slightly charred, about 3–5 minutes per side depending on thickness, until cooked through.
Remove the chicken from the grill and let it rest briefly, then slice or serve whole with cooked rice, lettuce leaves, ssamjang, scallions, sliced chiles, and sesame seeds for wrapping.