Make sure your beef is cut into either thin strips or small cubes. Refer to the top of the recipe for more information on what cut of beef to use for the lo mein. Add the beef, soy sauce, sesame oil, and brown sugar substitute to a mixing bowl. Fold the ingredients over until the brown sugar dissolves and the beef is coated.
Begin heating a wok or nonstick saute pan on high heat. When the wok is hot, add the beef. Cook and stir the beef at high heat until the beef browns and the sauce reduces and caramelizes onto the meat.
Transfer the beef to a safe place to rest and return the wok to your stove. Make the lo mein sauce by whisking together the beef broth, soy sauce, sesame oil, tapioca flour, onion powder, garlic powder, and chopped green onion. Leave the sauce aside while you prepare the next ingredients.
Thinly slice fresh celery and cabbage while you reheat your wok at high heat. Before any leftover sauce from the steak burns in your wok, add the vegetables. Cook the vegetables down until the cabbage is translucent and the celery is very soft. If the vegetables start to brown, add ¼ cup of water to the hot wok as needed until the vegetables cook down properly.
Drain your package of shirataki noodles and add the proper amount to your hot wok. Gently unravel the noodles with a spoon while they start to fry in the hot pan with the celery and cabbage. Once the noodles are golden brown all over, pour all the sauce you made in Step 3 into the wok.
Let the sauce bubble, thicken, and reduce for 1-2 minutes. Add the beef back to the wok, then stir the ingredients as the sauce continues to reduce. Once the sauce is thick and sticking to your noodles, your lo mein is ready to eat.