Cook the spaghetti: Boil spaghetti according to package instructions. Drain and set aside.
Sear the steak: Season steak with salt, pepper, garlic powder, and paprika. In a large skillet over medium-high heat, sear steak bites in olive oil until browned and cooked to your liking (about 3–5 minutes). Remove and set aside.
Wilt the spinach: In the same skillet, melt 1 tbsp butter. Add fresh spinach and sauté until just wilted, about 2–3 minutes. Remove and set aside with the steak.
Make the parmesan cream sauce: Melt remaining butter in the skillet. Add minced garlic and cook for 1 minute until fragrant. Stir in cream and milk. Let simmer and reduce for 3–4 minutes.
Add the cheese: Stir in parmesan until melted and silky. Adjust salt and pepper to taste.
Combine everything: Return steak, spinach, and spaghetti to the skillet. Toss gently to coat in the creamy, cheesy sauce.
Garnish and serve: Finish with fresh parsley, cracked black pepper, and red pepper flakes for extra flavor.