For the beef and marinade: Slice the partially frozen tenderloin as thin as possible using an extremely sharp knife; aim for 1/4-inch thickness.
In a food processor, combine the soy sauce, brown sugar, vegetable oil, red chile flakes, garlic, apples, ginger, onions and few grinds of black pepper. Cut 4 of the scallions into quarters and add to the food processor. Blend until smooth. Pour into a large resealable plastic bag. Add the sliced beef, and then squeeze out as much air as possible. Let marinate at room temperature for 1 hour.
Preheat a grill, grill pan or electric tabletop grill to medium-high heat. Remove the beef slices from the bag, shaking off any excess marinade. Cut the remaining scallions into 4-inch pieces.
When you are ready to eat, place the scallions on the grill, add the beef slices and cook the beef for 1 minute per side and the scallions until slightly charred. Remove to a platter.
For the lettuce wraps: Fill a lettuce leaf with some of the meat, carrots, sprouts, radishes, kimchi and grilled scallions. Serve with the hot sauce and Sesame Soy Dipping Sauce.
Sesame Soy Dipping Sauce:
Whisk together the soy sauce, rice vinegar, sesame oil and sesame seeds in a small bowl.