Preheat and prep: Heat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with olive oil or nonstick spray.

Cook the pasta: Boil fettuccine in well-salted water until just under al dente (about 1 minute less than package directions). Drain and toss with a little olive oil to prevent sticking.

Make the sauce base: In a large skillet or saucepan over medium heat, melt the butter. Add the garlic and cook 30–60 seconds until fragrant, not browned.

Add cream: Pour in the heavy cream and bring to a gentle simmer. Reduce heat to medium-low and cook 3–4 minutes, stirring, until slightly thickened.

Stir in cheeses: Add the Parmesan a handful at a time, stirring until smooth and melted. If using cream cheese, stir it in now until it dissolves. If the sauce seems too thick, whisk in a splash of chicken broth.

Season: Add salt, black pepper, Italian seasoning or parsley, and a pinch of red pepper flakes if you like. Taste and adjust. The sauce should be savory and well-balanced.

Combine: In a large bowl, mix the cooked fettuccine, chicken, and Alfredo sauce until everything is generously coated. If the mixture looks dry, add a bit more cream or broth.

Assemble the bake: Transfer the mixture to the prepared baking dish. Top with mozzarella and a light shower of extra Parmesan.

Bake: Bake 18–22 minutes until the sauce is bubbling at the edges and the cheese is melted. For more color, broil 1–2 minutes at the end, watching closely.

Rest and garnish: Let the bake sit 5 minutes to set. Sprinkle with fresh parsley and serve warm.