Pat steak cubes dry and season with salt and pepper.
Heat olive oil in cast iron skillet over high heat.
Add steak cubes in a single layer and sear for 2–3 minutes. Flip and cook another 1–2 minutes.
Remove steak and reduce heat to medium-low.
Add butter to pan, melt, and stir in garlic. Cook until fragrant.
Return steak to the pan and toss in butter and parsley until coated. Serve immediately.