Pat the steak dry. Use paper towels to remove surface moisture.
This helps the steak sear instead of steam.
Season generously. Toss the steak cubes with salt, pepper, smoked paprika, and red pepper flakes if using. Let them sit at room temperature for 10–15 minutes while you heat the pan.
Preheat the pan. Place a large heavy skillet (cast iron works best) over medium-high heat. Add the oil and let it get hot until it shimmers.
Sear in batches. Add half the steak in a single layer with space between pieces.
Don’t crowd the pan. Sear for 1–2 minutes per side until browned and just shy of your preferred doneness. Transfer to a plate and repeat with the remaining steak.
Make the garlic butter. Reduce heat to medium-low.
Add the butter to the pan. When melted, stir in the minced garlic. Cook for 30–45 seconds until fragrant, scraping up browned bits.
Bring it together. Return the steak (and any juices) to the pan.
Toss to coat in the garlic butter. Add lemon juice and half the parsley. Taste and adjust salt or pepper.
Finish and serve. Sprinkle with remaining parsley.
Serve hot with lemon wedges. If adding veggies like mushrooms or zucchini, sauté them briefly after searing the steak, then proceed with the garlic butter step.