Bring a large pot of salted water to a boil. Add spaghetti and cook until al dente, about 8-10 minutes. Drain and set aside.

Toss diced beef with Cajun seasoning. In a skillet, melt butter over medium-high heat, sear beef for 4-5 minutes until browned, then set aside.

In the same skillet, sauté minced garlic for 30 seconds. Add heavy cream, stir for 1-2 minutes. Then, add cream cheese, mozzarella, and parmesan, stirring until melted and smooth.

Return beef and spaghetti to the skillet, toss for 2 minutes, adding pasta water if needed for consistency.

Plate the dish, garnish with parsley, and serve hot, optionally adding more parmesan or Cajun seasoning.