Pat the steak dry with paper towels. Cut it into evenly sized pieces, approximately 1 inch each.
Season the steak bites with kosher salt and black pepper. Toss well to coat all sides.
Heat a large cast-iron skillet or heavy-bottomed frying pan over medium-high heat.
Add the olive oil to the hot skillet. Once the oil is shimmering, place the steak bites in a single layer.
Sear the steak for about 2 minutes without stirring to create a golden-brown crust.
Turn the steak pieces with tongs and cook for another 2 to 3 minutes, or until they reach your desired doneness. Cook the steak in batches if necessary to avoid overcrowding the pan.
Transfer the cooked steak bites to a clean plate and reduce the heat to medium-low.
Add the butter to the skillet. Once melted, add the minced garlic and cook for 30 seconds to 1 minute, stirring constantly until fragrant.
Stir in the Worcestershire sauce and red pepper flakes, if using.
Return the steak bites to the skillet and toss them in the garlic butter sauce until evenly coated.
Remove the skillet from the heat and sprinkle the steak bites with fresh parsley.
Serve immediately with mashed potatoes, rice, roasted vegetables, salad, or crusty bread.