Heat a large skillet over medium-high heat. Add olive oil if needed.
Add ground beef and cook until browned, breaking it up as it cooks.
Add garlic and ginger and cook for 30 seconds until fragrant.
Stir in soy sauce, sesame oil, keto-friendly sweetener, rice vinegar, black pepper, and red pepper flakes.
Reduce heat to medium and simmer for 5–7 minutes until the sauce thickens and coats the beef.
Stir in sesame seeds.
Spoon beef mixture into butter lettuce cups.
Serve immediately.