Rinse lettuce leaves and gently pat dry. Set aside to dry.
In a medium skillet over high heat, add the oil and brown the beef until cooked through. Drain and set aside. Reduce the heat to medium, in the same pan cook the onion until just softened. Add in the garlic, hoisin, soy sauce, ginger, and vinegar. Stir to combine. Toss in the water chestnuts, sesame oil, green onions and beef and stir until coated in sauce. Cook until heated through.
Arrange the lettuce leaves on a platter and fill each one with the beef mixture. Top with Sriracha sauce if you want and eat like a burrito!
Tip: You can find all of these items in you store's Asian aisle. Pickled ginger is the pink stuff you find next to your sushi. It comes in a jar and is very refreshing. Substitute 1 teaspoon of fresh ginger if you like.