Pat the shrimp dry. Moisture prevents browning, so use paper towels to blot them well. Season lightly with salt and pepper.
Sear the shrimp. Heat olive oil in a large skillet over medium-high.
Add shrimp in a single layer and cook 1–2 minutes per side, just until pink and opaque. Transfer to a plate.
Sauté the aromatics. Lower heat to medium. Add butter to the same skillet, then stir in garlic and red pepper flakes.
Cook 30–60 seconds until fragrant, not browned.
Deglaze and simmer. Pour in broth, scraping up browned bits. Stir in Italian seasoning and smoked paprika. Let it reduce for 2 minutes.
Add the cream and cheese. Reduce heat to low.
Stir in heavy cream and Parmesan until smooth. Simmer gently 2–3 minutes to thicken. Do not boil or the sauce may split.
Finish the dish. Return shrimp to the pan with any juices. Add lemon juice and parsley.
If using spinach or mushrooms, stir them in now and cook 1–2 minutes until wilted/tender. Taste and adjust salt and pepper.
Serve. Spoon over zucchini noodles, cauliflower rice, sautéed asparagus, or steamed broccoli. Garnish with extra Parmesan and lemon wedges.