Heat a medium skillet to high heat. Add 1 tablespoon of oil. Add ground beef. Break beef up into very small pieces with a metal spatula and reduce heat to medium. Cook until beef is fully cooked. Drain, remove from pan and allow beef to cool.
In the same pan add onions and stir fry for 1 minute. Add garlic, soy sauce, hoisin sauce, vinegar and chili pepper sauce to the onions. Stir to mix well. Stir in water chestnuts, green onions and sesame oil. Continue cooking for about 2 minutes. Add sauce mixture to ground beef and mix well in a bowl.
Pile the meat mixture into the center of each lettuce leaf. Wrap the lettuce around the meat like a burrito.