In a medium bowl, combine soy sauce, Worcestershire sauce, minced garlic, black pepper, onion powder, and a pinch of salt. Whisk together until well blended.

Place the beef sirloin strips in a shallow dish, pour the marinade over them, and coat evenly. Cover and let marinate for at least 15 minutes.

Heat a large skillet over medium-high heat and add olive oil. Allow the oil to warm for about 2 minutes.

Once the oil is hot, add the marinated beef strips in a single layer and sear for 3-4 minutes, then flip and cook for an additional 3-4 minutes.

Reduce heat to medium-low and add unsalted butter. Stir gently until melted, coating the beef with the creamy sauce.

Remove from heat and sprinkle with freshly chopped parsley. Transfer to a serving platter and drizzle any remaining buttery sauce over the top.