Bring a pot of salted water to a boil. Cook rotini until al dente according to package directions. Drain and set aside.
- Pat steak pieces dry and season with salt and pepper. Heat olive oil in a large skillet over medium-high heat and sear steak until browned and cooked to your liking. Remove from skillet and set aside.
- In the same skillet, reduce heat to medium. Add butter and garlic, cooking until fragrant, about 1 minute. Stir in red pepper flakes and optional seasonings.
- Add cooked rotini to the skillet and toss to coat in garlic butter. Return steak to the skillet and mix until combined and heated through.
- Sprinkle shredded mozzarella over the pasta. Cover skillet for 2–3 minutes until cheese melts and becomes gooey.
- Garnish with parsley and Parmesan before serving hot.