Begin by slicing your beef sirloin or ribeye into 1/8 inch thick pieces against the grain.

In a large mixing bowl, whisk together soy sauce, brown sugar, sesame oil, mirin, rice vinegar, grated Asian pear, minced garlic, freshly grated ginger, black pepper, and finely grated onion.

Add the thinly sliced beef to the marinade, ensuring each piece is well coated. Cover and refrigerate for at least 2 hours.

Heat a non-stick skillet or wok over medium-high heat and cook the marinated beef in small batches for 2-3 minutes per side.

Transfer the cooked beef bulgogi to a serving platter, garnish with toasted sesame seeds and green onions, and serve with cooked rice and lettuce leaves.