Preheat grill to medium-high heat. Meanwhile, make the Korean glaze. Combine soy sauce, mirin, brown sugar, sesame oil, onion powder, garlic powder, ginger powder, and 3/4 cup of water in a small saucepan over high heat. Bring to a boil, then reduce heat to a simmer for 3-4 minutes. Combine remaining 1 tablespoon water with cornstarch in a small bowl. Add half of the cornstarch slurry to sauce and let simmer one minute. If not thick enough, add remaining slurry and cook another minute.
Sprinkle lamb loin chops on all sides generously with Kosher salt. Grill until a rosy medium-rare. During the last minute of cooking, slather on Korean glaze. Meanwhile, brush scallions with canola oil and season with Kosher salt. Grill, turning once, until slightly charred in spots.
Serve Korean Lamb Chops with grilled scallions and extra Korean glaze, and top with chopped cilantro/parsley and sesame seeds. Devour.