Pat the sirloin steak cubes dry with paper towels to ensure a good sear.
Season the steak bites evenly with kosher salt and freshly ground black pepper.
Heat the olive oil in a large skillet over medium-high heat until shimmering.
Add the steak bites to the skillet in a single layer, making sure not to overcrowd the pan. Cook for 2-3 minutes without stirring to develop a crust.
Flip the steak bites and cook for another 2-3 minutes until browned and cooked to your desired doneness.
Reduce the heat to medium-low and add the unsalted butter to the skillet.
Once the butter has melted, add the minced garlic and cook for 1-2 minutes, stirring frequently, until fragrant and lightly golden.
Toss the steak bites in the garlic butter sauce to coat evenly.
Remove the skillet from heat and sprinkle the chopped fresh parsley over the steak bites.
Serve immediately while hot.