Step 1: Begin by preparing the bulgogi marinade. Grate the small pear, mince the garlic and ginger. In a large bowl, combine 90ml soy sauce, 30ml sesame oil, 30g minced garlic, 15g grated ginger, the grated pear, and 30g brown sugar substitute (10 min prep). Whisk thoroughly until well combined.

Step 2: Thinly slice the 900g beef round against the grain into bite-sized pieces (5 min prep). Add the sliced beef to the marinade, ensuring each piece is well coated. For best flavor and tenderness, ideally marinate for at least 30 minutes at room temperature, or longer in the refrigerator (not included in cook time).

Step 3: Prepare the Fermented Gochujang Aioli. In a separate bowl, whisk together 150g mayonnaise, 45g gochujang, 15ml rice vinegar, and 15ml lime juice until perfectly smooth and emulsified. Taste and adjust seasoning for balance of heat, tang, and umami (5 min prep). Set aside.

Step 4: Prepare the lettuce cups by washing and drying 18 large lettuce leaves. Thinly slice the 60g green onions for garnish (5 min prep). Have the 300g kimchi ready.

Step 5: Heat a large cast-iron skillet or grill pan over very high heat until smoking. Add a small amount of oil (not listed as ingredient, assume trace from cooking). Working in batches to avoid overcrowding, sear the marinated beef for 2-3 minutes per side until caramelized and cooked through (10 min cook). This precise searing is crucial for the bulgogi's flavor and texture. Remove cooked beef to a plate and repeat with remaining batches.