1In a large bowl, combine the soy sauce, sugar, sesame oil, and minced garlic.
Add the thinly sliced beef sirloin to the bowl and mix well to ensure the beef is evenly coated with the marinade.
Cover the bowl and let the beef marinate in the refrigerator for at least 30 minutes, or up to 2 hours for more flavor.
Heat a large skillet or grill pan over medium-high heat.
Add the marinated beef to the skillet and cook for 2-3 minutes on each side, or until the beef is cooked through and slightly caramelized.
Remove the beef from the skillet and transfer to a serving plate.
Garnish with chopped green onions and sesame seeds.
Serve hot with steamed rice or lettuce wraps.