In a large skillet, heat oil over medium heat. Sauté tofu, mushrooms, onion, water chestnuts, and celery 2 to 3 minutes until soft.
Reduce heat to medium, and stir in cashews, teriyaki sauce, vinegar, and vegetable stock. Simmer 2 to 3 minutes.
Spoon tofu mixture into the center of each piece of lettuce leaf and drizzle with tamari or soy sauce, if desired. Wrap the lettuce around the filling and eat like a taco.
The tofu filling is equally delicious in a corn or flour tortilla.