Preheat and prep: Heat the oven to 425°F (220°C).
Pat the steak cubes dry with paper towels. Dry steak browns better and faster.
Season the steak: Toss the steak with 1 tablespoon olive oil, 1/2 teaspoon salt, black pepper, and smoked paprika if using. Set aside while you start the broccoli.
Roast the broccoli: On a large sheet pan, toss broccoli with 2 tablespoons olive oil and 1/2 teaspoon salt.
Spread out in a single layer. Roast for 18–22 minutes, flipping once, until the edges are browned and crisp.
Heat the skillet: While the broccoli roasts, place a large heavy skillet (cast iron is ideal) over medium-high heat. Let it get hot—really hot.
A drop of water should sizzle instantly.
Sear the steak bites: Add the steak in a single layer without crowding. Sear 2–3 minutes per side until well browned and just cooked through. Work in batches if needed.
Transfer to a plate and tent loosely with foil.
Make garlic butter: Lower the heat to medium. Add butter to the skillet. When melted and foamy, add minced garlic and red pepper flakes.
Stir for 30–45 seconds until fragrant—don’t let the garlic brown.
Glaze the steak: Return steak to the skillet with any juices. Toss in the garlic butter for 30–60 seconds. Add lemon juice and parsley.
Taste and adjust salt.
Serve: Plate the crispy broccoli and top with steak bites. Spoon extra garlic butter from the pan over everything. Finish with a squeeze of fresh lemon.