Spread zucchini noodles on paper towels and blot well to remove excess moisture.
Pat steak dry. Toss with salt, pepper, and smoked paprika to coat.
Heat olive oil in a large skillet over medium-high heat until shimmering.
Sear steak in two batches, 2–3 minutes per batch, until browned. Transfer to a plate.
Reduce heat to medium. Melt butter, then stir in garlic and red pepper flakes for 30 seconds.
Pour in beef broth and lemon juice. Scrape up browned bits and simmer 1 minute. Stir in Italian seasoning.
Add zucchini noodles and toss just until barely tender, 1–2 minutes. Do not overcook.
Return steak and juices to the pan. Toss with Parmesan and parsley. Adjust seasoning and serve hot.