Pat the steak cubes dry with paper towels. This ensures proper searing.
In a bowl, toss steak with olive oil, salt, pepper, and paprika (if using) until evenly coated.
Heat a large cast iron skillet or heavy pan over high heat until very hot, about 2 minutes.
Add steak bites to the hot pan in a single layer, working in batches if necessary to avoid overcrowding.
Sear for 45 seconds to 1 minute per side without moving them too much, until browned on all sides and cooked to desired doneness.
Transfer seared steak bites to a clean plate and reduce heat to medium-low.
Add butter to the same pan and allow it to melt.
Once butter is melted, add minced garlic and cook for 30-60 seconds until fragrant, being careful not to burn it.
Stir in thyme and red pepper flakes (if using).
Return the steak bites to the pan along with any accumulated juices. Toss to coat evenly in the garlic butter sauce.
If using, add lemon juice and toss again.
Remove from heat and sprinkle with fresh parsley before serving.
Serve immediately while hot.
