Combined lime juice, fish sauce, soy sauce, chili garlic sauce (from your Asian market, I like the one with the roster on it with the green lid), Mirin, sugar, ginger and garlic. Mix well and set aside while you prepare the noodles.
Heat enough water in a bowl to cover the noodle bundles. The water should be hot but not boiling. Set aside. Noodle should be soft in about 15 minutes, more or less.
Pork or Shrimp or Tofu:
Heat a nonstick skillet on medium high heat. Add pork and break it up as it browns. Continue to cook and break up until all the pork is cooked (no pinkness). You can grate a bit of ginger and garlic into the meat to boost the flavor. You can also add about one teaspoon of chili garlic sauce. If using shrimp cook the same way make sure you do not overcook! It will make the shrimp tough.
Add the oil to wok or sauté pan and heat on medium high. Add onion and mushrooms, sauté 2-3 mins, remove from pan. Add pork to pan and cook, remove from pan. Pour dressing in pan heat to just below boiling, turn heat down medium low. Add noodles and mix them in the sauce. Add back onion, mushroom, pork, then add green onion bottoms, carrot, celery and mix well. On a plate place lettuce, cucumber, green onion tops and tomatoes if used. Using tongs or spoon place the noodle mixture on top of the lettuce. Serve immediately. You can garnish the mixture with chilies, peanuts, mint leaves, cilantro leaves or sliced lime.