Prep the beef: Slice the steak as thinly as possible, against the grain. If it’s not pre-sliced, pop it in the freezer for 20 minutes first to make slicing easier.
Heat the skillet: Warm 1 tablespoon oil in a large cast-iron or stainless skillet over medium-high heat until shimmering.
Sauté veggies: Add onions and peppers with a pinch of salt.
Cook 6–8 minutes, stirring occasionally, until tender and starting to caramelize. If using mushrooms, add them in the last 4 minutes. Transfer veggies to a plate.
Cook the beef: Add remaining oil to the skillet.
Season beef with half the salt and pepper. Spread in a single layer and sear 2–3 minutes, stirring once or twice, until just cooked through. Don’t overcrowd; work in batches if needed.
Add flavor: Stir in garlic, smoked paprika, Italian seasoning, remaining salt and pepper, and Worcestershire.
Cook 30–60 seconds until fragrant.
Combine: Return peppers and onions to the pan and toss with the beef. Reduce heat to medium-low.
Make it cheesy: Lay provolone slices over the mixture, or sprinkle shredded cheese evenly. If using cream cheese, dot it around the skillet.
Cover for 1–2 minutes to melt.
Finish and serve: Garnish with parsley. Serve as-is, or with low-carb sides like cauliflower rice, zucchini noodles, or a simple salad.