Remove the steak from the refrigerator and let it sit at room temperature for about 1 hour. Then, cut the steak into 1-inch cubes and pat them dry with paper towels.
Season the steak cubes generously with salt and any additional spices you prefer.
Heat a large cast iron pan over medium-high heat and add enough neutral oil to coat the bottom of the pan.
Sear the steak cubes in batches, cooking for about 2 minutes on each side until browned. Remove the seared steak from the pan and set it aside.
In the same pan, remove most of the oil, leaving just enough to sauté. Add minced garlic and shallots, cooking until fragrant.
Add unsalted butter to the pan and let it melt, mixing it with the sautéed garlic and shallots.
Return the seared steak to the pan and toss to warm through, adjusting seasoning with salt and pepper as needed.
Mix in minced green onions and parsley, tossing everything together before serving.
Serve immediately, garnished with additional green onions and parsley. For a spicy kick, sprinkle with crushed red pepper flakes, if desired.