Cook pasta in a large pot of salted boiling water according to package directions until al dente. Reserve 1/2 cup of pasta water, then drain.
Season sliced beef strips with salt and pepper.
Heat olive oil in a large skillet over high heat. Sear beef in batches until browned, approximately 2 minutes per side. Remove beef from the skillet and set aside.
Reduce heat to medium. Add butter to the same skillet. Once melted, add minced garlic and red pepper flakes. Sauté for 60-90 seconds until fragrant.
Add the cooked pasta and reserved pasta water to the skillet. Toss thoroughly to emulsify the butter and water into a light sauce.
Return the beef to the skillet. Add chopped parsley and grated Parmesan cheese.
Toss until the cheese is melted and the ingredients are evenly distributed. Serve immediately.