Begin by cutting your sirloin into even 1-inch chunks to ensure they cook at the same rate. Thoroughly pat the cubed sirloin steak dry with paper towels. Season the steak chunks generously with the kosher salt and black pepper.

Place your round black cast-iron skillet over medium-high heat. Allow the dry pan to heat up for about 3 to 4 minutes until it is screaming hot and begins to lightly smoke. Pour in the avocado oil.

Carefully add the cubed sirloin steak to the hot oil in a single, even layer. Let the chunks sizzle undisturbed for exactly 2 minutes to form a dark brown caramelized crust. Flip and sear for an additional 1 to 2 minutes.

Reduce the stove's heat to low. Add the unsalted butter and the minced garlic to the center of the skillet. As the butter melts into a glossy yellow pool, tilt the pan slightly and baste the steak chunks continually for 45 seconds.

Toss the steak bites directly in the pan to ensure they are fully coated. Sprinkle the finely chopped vibrant green parsley flakes evenly over the top. Serve immediately, clustered together inside the warm cast-iron skillet.