Fill a large pot with salted water and bring to a boil. Add spaghetti and cook until al dente. Reserve ½ cup of pasta water before draining.
Pat steak pieces dry and season with salt, pepper, and garlic powder. Heat olive oil in a skillet and sear steak on all sides for 1–2 minutes. Remove and set aside.
In the same skillet, melt butter and sauté minced garlic for 30 seconds until fragrant.
Pour in heavy cream, scraping up browned bits. Add Parmesan cheese, Italian seasoning, and red pepper flakes. Stir until smooth.
Add roasted red peppers, then return steak and pasta to the skillet. Toss to coat evenly in sauce.
Adjust consistency with reserved pasta water. Garnish with parsley and serve hot.
