Cook the spaghetti or linguine according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of pasta water.

In a large skillet over medium-high heat, melt 2 tablespoons of butter. Season the steak strips with salt and pepper, then add them to the skillet in a single layer. Cook for about 2-3 minutes until browned, then flip and cook for another 2-3 minutes until cooked through. Remove the steak from the skillet and set aside.

In the same skillet, add the remaining 2 tablespoons of butter and minced garlic. Sauté for about 1 minute until fragrant, being careful not to burn the garlic.

Add the cooked noodles to the skillet along with the soy sauce, Worcestershire sauce, and red pepper flakes (if using). Toss to combine, adding reserved pasta water as needed to create a light sauce.

Return the cooked steak to the skillet and toss everything together until well combined and heated through.

Serve immediately, garnished with sliced green onions and chopped parsley.