1. To make Filling: Heat oil in large skillet over medium heat. Add onion, ginger, lemongrass, and garlic, and cook 7 to 10 minutes, or until onions are soft and beginning to brown. Add tofu and water chestnuts, breaking tofu into small crumbles; cook 4 minutes, or until heated through. Stir in soy sauce, hoisin sauce, and chile sauce. Transfer to serving bowl.
2. Place lettuce leaves on platter, and set out garnishes in small serving bowls. Let guests wrap tofu mixture in lettuce leaves, and top with their choice of garnishes.