Cook the Pasta: Boil the spaghetti according to the package instructions. Save ¼ cup of pasta water before draining. Set aside.
Brown the Beef: In a large skillet, heat olive oil over medium heat. Add ground beef and cook until browned. Drain excess fat. Stir in diced onion, minced garlic, Italian seasoning, salt, pepper, and red pepper flakes. Cook for 3-4 minutes until fragrant.
Make the Sauce: Lower the heat and add butter, heavy cream, Parmesan cheese, garlic powder, salt, pepper, and lemon juice. Stir continuously until smooth and creamy.
Combine: Add the cooked spaghetti to the skillet with the beef mixture. Toss to combine, adding reserved pasta water to adjust the sauce consistency.
Serve: Garnish with chopped parsley and additional Parmesan cheese. Serve immediately and enjoy!