Heat the olive oil in a large skillet over medium-high heat.

Add the diced onion and cook for 3 minutes until softened.

Add the ground beef and minced garlic. Cook for 5 to 7 minutes, breaking the meat apart until browned and fully cooked. Drain excess fat.

Stir in the hoisin sauce, soy sauce, rice vinegar, and sesame oil. Simmer for 2 minutes to coat the beef evenly.

Remove from heat and stir in the chopped green onions.

Spoon the beef mixture into the center of the butter lettuce leaves and serve immediately.