Season the cubed sirloin steak with Cajun seasoning, salt, and pepper. Let it marinate for at least 15 minutes to absorb the flavors.
In a large skillet, heat the olive oil over medium-high heat until it shimmers.
Add the seasoned steak bites to the skillet in a single layer. Cook for 2-3 minutes on each side, or until they develop a nice crust and reach your desired doneness. Avoid overcrowding the pan; work in batches if necessary. Remove the steak bites and set them aside.
In the same skillet, lower the heat to medium and add the butter. Once melted, stir in the minced garlic and cook for about 30 seconds until fragrant.
Return the steak bites to the skillet, tossing them in the Cajun butter to coat evenly for 1-2 minutes. If desired, add a squeeze of fresh lemon juice to brighten flavors.
Sprinkle fresh chopped parsley over the steak bites before serving.
Notes
Serve hot on a platter, garnished with additional parsley and lemon wedges.