Open the shirataki noodle packages and drain them in a colander. Rinse under cold running water for at least 1 minute.

Heat a dry skillet over medium-high heat. Add the rinsed noodles and toast for 2 minutes, stirring occasionally, until most of the visible moisture has evaporated and the noodles look dry. Transfer to a bowl and set aside.

Pat the beef strips completely dry with paper towels. Season with a pinch of salt and pepper.

Heat 1 tablespoon of avocado oil in the same skillet over high heat until shimmering. Add half the beef strips in a single layer. Sear for 1 to 2 minutes per side until browned, then transfer to a plate. Repeat with the remaining beef.

Reduce heat to medium. Add the remaining tablespoon of oil to the skillet. Add the onion and cook for 3 minutes, stirring often, until softened and lightly golden.

Add the mushrooms and cook for 4 to 5 minutes without stirring too often, until browned on the edges and tender.

Add the garlic and smoked paprika. Stir and cook for 30 seconds until fragrant.

Pour in the beef broth, Worcestershire sauce, and Dijon mustard. Stir to combine and scrape up any browned bits from the bottom of the pan.

Simmer for 4 to 5 minutes until the broth reduces by about a third. If using xanthan gum, whisk it in now and stir until the sauce thickens slightly, about 30 seconds.

Remove the skillet from the heat. Stir in the sour cream until the sauce is smooth and creamy. Taste and adjust salt.

Return the seared beef and any resting juices to the skillet. Add the toasted shirataki noodles and toss gently to coat everything in the sauce.

Return the skillet to very low heat for 1 to 2 minutes just to warm the noodles through. Do not boil.

Divide between four plates and top with chopped fresh parsley. Serve immediately.