Heat a large skillet over medium-high heat and add the olive oil.

Add the sliced beef in an even layer and cook, stirring only as needed, until browned, about 3 to 4 minutes. Transfer the beef and any juices to a plate.

In the same skillet, add the diced onion and minced garlic. Cook, stirring, until softened and fragrant, about 2 to 3 minutes.

Add the sliced mushrooms and cook, stirring occasionally, until they release their moisture and turn golden, about 5 minutes.

Pour in the beef broth and scrape up any browned bits from the bottom of the skillet with a spoon. Bring to a gentle simmer.

Stir in the heavy cream, Dijon mustard, and Worcestershire sauce until smooth. Season with salt and black pepper and simmer 2 to 3 minutes until slightly thickened.

Return the browned beef and any accumulated juices to the skillet, stir to coat in the sauce, and simmer for 5 minutes until the beef is heated through and the sauce thickens to a spoon-coating consistency.

Warm the zucchini noodles or cauliflower rice in a separate pan or microwave until hot.

Serve the creamy beef mixture over the zucchini noodles or cauliflower rice and garnish with chopped fresh parsley.