1 head lettuce (Bibb, Boston, and butter are great choices)
1 lb lean ground beef
1/2 cup brown sugar (or less to decrease sweetness)
1/4 cup soy sauce or tamari
1 tbsp sesame oil; divided in half
3 cloves garlic; minced/grated
1/4 tsp. ground ginger
1/8 tsp. red pepper flakes (optional and to taste)
1 bunch green onions; divided between white and green parts
3 tbsp rice wine vinegar
Sesame seeds for garnish (optional)