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.
Whisk together the soy sauce, rice vinegar, sesame oil and sesame seeds in a small bowl.