Fill a large pot with salted water and bring to a rolling boil. Cook penne until just tender. Drain and set aside, reserving 1/2 cup of pasta water.

In a bowl, toss the sirloin strips with olive oil, Cajun seasoning, garlic powder, smoked paprika, salt, and black pepper until evenly coated.

Heat a large skillet over medium-high heat. Add 2 tablespoons butter and let it foam. Add steak in a single layer and sear for 2 to 3 minutes per side until browned but still slightly pink. Remove steak to a plate.

Add minced garlic to the hot pan and cook about 30 seconds, scraping up browned bits. Remove the garlic with the steak so it does not burn.

In the same skillet, melt 1 tablespoon butter. Sprinkle in flour (about 1 tablespoon) and whisk to form a roux. Cook for 1 minute to remove raw flour taste.

Slowly whisk in heavy cream and whole milk until smooth. Bring to a gentle simmer and cook for 3 to 5 minutes until the mixture thickens slightly.

Reduce heat to low. Stir in mozzarella, Parmesan, and cream cheese. Stir constantly until the cheeses melt and the sauce becomes glossy and thick.

Season the sauce with 1 tsp garlic powder, 1/2 tsp onion powder, and extra salt and pepper to taste. If the sauce is too thick, loosen with a splash of the reserved pasta water to reach desired consistency.

Add the cooked penne to the skillet and toss to coat evenly. Top the sauced pasta with the seared Cajun steak. Garnish with chopped parsley or sliced green onions as desired.