Rinse lettuce leaves, keeping them whole. Set aside to drain. Cook venison in a large skillet over medium heat, stirring often to break up the meat. Add onion, garlic, soy sauce, hoisin sauce, ginger, vinegar, and chili sauce. Cook until the meat is crumbled and brown. Add water chestnuts or bamboo shoots and green onions. Cook until onions begin to wilt, about 2 minutes. Stir in sesame oil. Arrange lettuce leaves on the outer edge of a platter. Spoon meat mixture into center of the lettuce leaves and eat like a taco.