Bring a large pot of salted water to a boil. Add the fettuccine pasta and cook according to package instructions until al dente. Drain and set aside.
While the pasta cooks, season the steak bites with kosher salt and freshly ground black pepper.
Heat olive oil in a large skillet over medium-high heat until shimmering.
Add the steak bites in a single layer and cook without stirring for 2-3 minutes to develop a sear.
Stir and continue cooking for another 2-3 minutes until the steak bites are browned on all sides and cooked to your preferred doneness. Remove the steak bites from the skillet and set aside.
In the same skillet, reduce heat to medium and add the minced garlic and crushed red pepper flakes. Sauté for about 1 minute until fragrant, being careful not to burn the garlic.
Add the unsalted butter to the skillet and let it melt.
Pour in the heavy cream and bring to a gentle simmer, stirring frequently.
Gradually whisk in the grated Parmesan cheese until the sauce is smooth and creamy.
Season the sauce with salt and freshly ground black pepper to taste.
Add the cooked fettuccine pasta to the skillet and toss to coat the pasta evenly with the garlic parmesan sauce.
Return the steak bites to the skillet and gently toss to combine everything.
Sprinkle the chopped fresh parsley over the dish and serve immediately.