Step 1: Partially freeze the ribeye for 30-45 minutes to make it easier to slice thinly across the grain.
Step 2: In a large bowl, whisk together the soy sauce, brown sugar, grated pear, garlic, ginger, sesame oil, and black pepper.
Step 3: Add the thinly sliced beef to the marinade and toss by hand to ensure every piece is thoroughly coated.
Step 4: Transfer the meat and marinade to a sealed container and refrigerate for at least 4 hours, or ideally overnight.
Step 5: Heat a large cast-iron skillet or grill pan over high heat until it begins to smoke slightly.
Step 6: Cook the beef in small batches for 1-2 minutes per side until charred and caramelized. Do not overcrown the pan.
Step 7: Garnish with chopped green onions and toasted sesame seeds, then serve immediately with lettuce wraps and rice.