Start by choosing the right cut of beef. The most commonly used cuts for bulgogi are sirloin, rib-eye, or tenderloin. These cuts are tender and have a good amount of marbling, which adds flavor and juiciness to the dish.
Slice the beef thinly against the grain. This ensures that the meat remains tender and easy to chew after cooking.
In a bowl, combine the soy sauce, sesame oil, minced garlic, grated ginger, brown sugar, and either grated pear or kiwi. Mix well until the sugar has dissolved.
Place the sliced beef into a resealable plastic bag or a shallow dish. Pour the marinade over the beef, making sure it is well coated. Seal the bag or cover the dish with plastic wrap and let it marinate in the refrigerator for at least 1 hour, but preferably overnight.
When you're ready to cook, remove the beef from the marinade and discard any excess liquid. Allow the beef to come to room temperature before cooking.
Heat a grill or a large skillet over medium-high heat. Add a drizzle of oil to prevent sticking. Working in batches, cook the beef for about 2-3 minutes per side, or until it is cooked through and slightly caramelized.
Once cooked, transfer the beef to a serving platter and garnish with sesame seeds and thinly sliced green onions. Serve immediately and enjoy!