Preheat Oven: Preheat oven to 350°F (175°C). Grease a 9×13 baking dish.
Cook Veggies: In a large skillet, melt butter over medium heat. Sauté onion and garlic until fragrant, then add mushrooms and cook until tender.
Make Sauce: Stir in heavy cream (or milk), chicken broth, Parmesan, thyme, salt, and pepper. Simmer until slightly thickened.
Combine: Add cooked pasta and shredded chicken to the sauce, mixing until everything is coated.
Bake: Pour mixture into the prepared baking dish. Top with shredded mozzarella or cheddar. Bake for 20–25 minutes until bubbly and golden on top.
Serve: Garnish with chopped parsley if desired.
